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 $113.78   11.241%   $126.57   $126.57   $126.55   $126.60  
  Purchase #2 $126.86   9.112%   $138.4195   $138.42   $138.40   $138.40  
  Purchase #3 $77.30   4.136%   $80.4971   $80.50   $80.50   $80.50  
  Purchase #4 $191.62   6.241%   $203.579   $203.58   $203.60   $203.60  
  Purchase #5 $247.42   3.231%   $255.4141   $255.41   $255.40   $255.40  
  Purchase #6 $149.53   4.211%   $155.8267   $155.83   $155.85   $155.80  
  Purchase #7 $170.68   9.162%   $186.3177   $186.32   $186.30   $186.30  
  7 purchase totals = $1,077.19       $1,146.6241   $1,146.63   $1,146.60   $1,146.60