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 $71.40   5.825%   $75.5591   $75.56   $75.55   $75.60  
  Purchase #2 $142.42   11.288%   $158.4964   $158.50   $158.50   $158.50  
  Purchase #3 $141.36   4.559%   $147.8046   $147.80   $147.80   $147.80  
  Purchase #4 $223.59   9.294%   $244.3705   $244.37   $244.35   $244.40  
  Purchase #5 $243.48   9.635%   $266.9393   $266.94   $266.95   $266.90  
  Purchase #6 $58.56   10.257%   $64.5665   $64.57   $64.55   $64.60  
  Purchase #7 $116.83   8.665%   $126.9533   $126.95   $126.95   $127.00  
  7 purchase totals = $997.64       $1,084.6897   $1,084.69   $1,084.65   $1,084.80