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 $89.88   6.444%   $95.6719   $95.67   $95.65   $95.70  
  Purchase #2 $236.92   8.287%   $256.5536   $256.55   $256.55   $256.60  
  Purchase #3 $8.56   7.392%   $9.1928   $9.19   $9.20   $9.20  
  Purchase #4 $189.82   6.635%   $202.4146   $202.41   $202.40   $202.40  
  Purchase #5 $229.48   3.762%   $238.113   $238.11   $238.10   $238.10  
  Purchase #6 $85.50   8.214%   $92.523   $92.52   $92.50   $92.50  
  Purchase #7 $60.87   6.321%   $64.7176   $64.72   $64.70   $64.70  
  7 purchase totals = $901.03       $959.1865   $959.17   $959.10   $959.20