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 $61.46   4.268%   $64.0831   $64.08   $64.10   $64.10  
  Purchase #2 $224.43   9.626%   $246.0336   $246.03   $246.05   $246.00  
  Purchase #3 $64.71   7.530%   $69.5827   $69.58   $69.60   $69.60  
  Purchase #4 $58.69   6.784%   $62.6715   $62.67   $62.65   $62.70  
  Purchase #5 $245.85   3.494%   $254.44   $254.44   $254.45   $254.40  
  Purchase #6 $121.32   7.409%   $130.3086   $130.31   $130.30   $130.30  
  Purchase #7 $106.27   7.377%   $114.1095   $114.11   $114.10   $114.10  
  7 purchase totals = $882.73       $941.2290   $941.22   $941.25   $941.20