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 $52.38   10.843%   $58.0596   $58.06   $58.05   $58.10  
  Purchase #2 $243.94   6.217%   $259.1057   $259.11   $259.10   $259.10  
  Purchase #3 $233.34   5.665%   $246.5587   $246.56   $246.55   $246.60  
  Purchase #4 $78.72   11.713%   $87.9405   $87.94   $87.95   $87.90  
  Purchase #5 $52.36   3.768%   $54.3329   $54.33   $54.35   $54.30  
  Purchase #6 $160.86   3.809%   $166.9872   $166.99   $167.00   $167.00  
  Purchase #7 $131.77   8.344%   $142.7649   $142.76   $142.75   $142.80  
  7 purchase totals = $953.37       $1,015.7495   $1,015.75   $1,015.75   $1,015.80