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 $62.97   9.202%   $68.7645   $68.76   $68.75   $68.80  
  Purchase #2 $99.80   8.346%   $108.1293   $108.13   $108.15   $108.10  
  Purchase #3 $219.49   8.693%   $238.5703   $238.57   $238.55   $238.60  
  Purchase #4 $151.70   11.418%   $169.0211   $169.02   $169.00   $169.00  
  Purchase #5 $125.40   8.338%   $135.8559   $135.86   $135.85   $135.90  
  Purchase #6 $230.58   11.706%   $257.5717   $257.57   $257.55   $257.60  
  Purchase #7 $68.32   11.141%   $75.9315   $75.93   $75.95   $75.90  
  7 purchase totals = $958.26       $1,053.8443   $1,053.84   $1,053.80   $1,053.90