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 $38.71   11.676%   $43.2298   $43.23   $43.25   $43.20  
  Purchase #2 $226.96   6.614%   $241.9711   $241.97   $241.95   $242.00  
  Purchase #3 $179.63   8.854%   $195.5344   $195.53   $195.55   $195.50  
  Purchase #4 $66.73   10.488%   $73.7286   $73.73   $73.75   $73.70  
  Purchase #5 $157.58   12.103%   $176.6519   $176.65   $176.65   $176.70  
  Purchase #6 $95.54   13.346%   $108.2908   $108.29   $108.30   $108.30  
  Purchase #7 $211.28   12.703%   $238.1189   $238.12   $238.10   $238.10  
  7 purchase totals = $976.43       $1,077.5255   $1,077.52   $1,077.55   $1,077.50