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 $125.48   8.272%   $135.8597   $135.86   $135.85   $135.90  
  Purchase #2 $148.69   11.615%   $165.9603   $165.96   $165.95   $166.00  
  Purchase #3 $73.86   8.731%   $80.3087   $80.31   $80.30   $80.30  
  Purchase #4 $102.61   4.832%   $107.5681   $107.57   $107.55   $107.60  
  Purchase #5 $244.56   12.703%   $275.6265   $275.63   $275.65   $275.60  
  Purchase #6 $213.49   7.666%   $229.8561   $229.86   $229.85   $229.90  
  Purchase #7 $33.95   8.810%   $36.941   $36.94   $36.95   $36.90  
  7 purchase totals = $942.64       $1,032.1204   $1,032.13   $1,032.10   $1,032.20