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 $65.54   13.236%   $74.2149   $74.21   $74.20   $74.20  
  Purchase #2 $218.38   6.862%   $233.3652   $233.37   $233.35   $233.40  
  Purchase #3 $91.99   6.501%   $97.9703   $97.97   $97.95   $98.00  
  Purchase #4 $222.43   6.825%   $237.6108   $237.61   $237.60   $237.60  
  Purchase #5 $5.27   12.700%   $5.9393   $5.94   $5.95   $5.90  
  Purchase #6 $111.72   11.278%   $124.3198   $124.32   $124.30   $124.30  
  Purchase #7 $243.94   8.284%   $264.148   $264.15   $264.15   $264.10  
  7 purchase totals = $959.27       $1,037.5683   $1,037.57   $1,037.50   $1,037.50