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 $240.97   8.113%   $260.5199   $260.52   $260.50   $260.50  
  Purchase #2 $51.29   5.682%   $54.2043   $54.20   $54.20   $54.20  
  Purchase #3 $165.56   4.533%   $173.0648   $173.06   $173.05   $173.10  
  Purchase #4 $120.73   8.341%   $130.8001   $130.80   $130.80   $130.80  
  Purchase #5 $218.95   11.116%   $243.2885   $243.29   $243.30   $243.30  
  Purchase #6 $178.72   8.191%   $193.359   $193.36   $193.35   $193.40  
  Purchase #7 $172.27   12.320%   $193.4937   $193.49   $193.50   $193.50  
  7 purchase totals = $1,148.49       $1,248.7303   $1,248.72   $1,248.70   $1,248.80