Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $201.99   12.176%   $226.5843   $226.58   $226.60   $226.60  
  Purchase #2 $127.64   12.589%   $143.7086   $143.71   $143.70   $143.70  
  Purchase #3 $131.52   13.334%   $149.0569   $149.06   $149.05   $149.10  
  Purchase #4 $200.78   12.219%   $225.3133   $225.31   $225.30   $225.30  
  Purchase #5 $23.26   11.361%   $25.9026   $25.90   $25.90   $25.90  
  Purchase #6 $194.68   8.363%   $210.9611   $210.96   $210.95   $211.00  
  Purchase #7 $168.82   4.589%   $176.5671   $176.57   $176.55   $176.60  
  7 purchase totals = $1,048.69       $1,158.0939   $1,158.09   $1,158.05   $1,158.20