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 $88.39   8.264%   $95.6945   $95.69   $95.70   $95.70  
  Purchase #2 $130.75   6.179%   $138.829   $138.83   $138.85   $138.80  
  Purchase #3 $143.94   13.201%   $162.9415   $162.94   $162.95   $162.90  
  Purchase #4 $24.52   4.673%   $25.6658   $25.67   $25.65   $25.70  
  Purchase #5 $116.26   3.225%   $120.0094   $120.01   $120.00   $120.00  
  Purchase #6 $239.26   7.426%   $257.0274   $257.03   $257.05   $257.00  
  Purchase #7 $108.93   13.143%   $123.2467   $123.25   $123.25   $123.20  
  7 purchase totals = $852.05       $923.4143   $923.42   $923.45   $923.30