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 $63.47   5.726%   $67.1043   $67.10   $67.10   $67.10  
  Purchase #2 $53.54   10.128%   $58.9625   $58.96   $58.95   $59.00  
  Purchase #3 $114.68   10.568%   $126.7994   $126.80   $126.80   $126.80  
  Purchase #4 $240.54   5.617%   $254.0511   $254.05   $254.05   $254.10  
  Purchase #5 $246.31   8.702%   $267.7439   $267.74   $267.75   $267.70  
  Purchase #6 $33.82   9.415%   $37.0042   $37.00   $37.00   $37.00  
  Purchase #7 $168.83   4.528%   $176.4746   $176.47   $176.45   $176.50  
  7 purchase totals = $921.19       $988.1400   $988.12   $988.10   $988.20