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 $92.47   5.640%   $97.6853   $97.69   $97.70   $97.70  
  Purchase #2 $218.27   12.685%   $245.9575   $245.96   $245.95   $246.00  
  Purchase #3 $119.38   13.572%   $135.5823   $135.58   $135.60   $135.60  
  Purchase #4 $102.57   8.126%   $110.9048   $110.90   $110.90   $110.90  
  Purchase #5 $162.74   9.628%   $178.4086   $178.41   $178.40   $178.40  
  Purchase #6 $31.95   7.478%   $34.3392   $34.34   $34.35   $34.30  
  Purchase #7 $207.96   5.222%   $218.8197   $218.82   $218.80   $218.80  
  7 purchase totals = $935.34       $1,021.6974   $1,021.70   $1,021.70   $1,021.70