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 $75.55   11.163%   $83.9836   $83.98   $84.00   $84.00  
  Purchase #2 $199.30   13.578%   $226.361   $226.36   $226.35   $226.40  
  Purchase #3 $121.86   3.385%   $125.985   $125.99   $126.00   $126.00  
  Purchase #4 $246.52   3.754%   $255.7744   $255.77   $255.75   $255.80  
  Purchase #5 $84.91   12.545%   $95.562   $95.56   $95.55   $95.60  
  Purchase #6 $80.86   4.570%   $84.5553   $84.56   $84.55   $84.60  
  Purchase #7 $23.83   4.319%   $24.8592   $24.86   $24.85   $24.90  
  7 purchase totals = $832.83       $897.0805   $897.08   $897.05   $897.30