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 $149.27   13.415%   $169.2946   $169.29   $169.30   $169.30  
  Purchase #2 $111.80   13.691%   $127.1065   $127.11   $127.10   $127.10  
  Purchase #3 $182.40   11.684%   $203.7116   $203.71   $203.70   $203.70  
  Purchase #4 $238.67   5.617%   $252.0761   $252.08   $252.10   $252.10  
  Purchase #5 $194.78   10.134%   $214.519   $214.52   $214.50   $214.50  
  Purchase #6 $58.47   7.733%   $62.9915   $62.99   $63.00   $63.00  
  Purchase #7 $63.31   4.568%   $66.202   $66.20   $66.20   $66.20  
  7 purchase totals = $998.70       $1,095.9013   $1,095.90   $1,095.90   $1,095.90