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 $85.54   12.852%   $96.5336   $96.53   $96.55   $96.50  
  Purchase #2 $48.43   7.400%   $52.0138   $52.01   $52.00   $52.00  
  Purchase #3 $40.53   8.771%   $44.0849   $44.08   $44.10   $44.10  
  Purchase #4 $171.56   10.376%   $189.3611   $189.36   $189.35   $189.40  
  Purchase #5 $156.95   8.225%   $169.8591   $169.86   $169.85   $169.90  
  Purchase #6 $220.62   11.152%   $245.2235   $245.22   $245.20   $245.20  
  Purchase #7 $172.72   3.597%   $178.9327   $178.93   $178.95   $178.90  
  7 purchase totals = $896.35       $976.0087   $975.99   $976.00   $976.00