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 $244.36   13.401%   $277.1067   $277.11   $277.10   $277.10  
  Purchase #2 $93.46   3.284%   $96.5292   $96.53   $96.55   $96.50  
  Purchase #3 $87.55   7.575%   $94.1819   $94.18   $94.20   $94.20  
  Purchase #4 $210.83   11.746%   $235.5941   $235.59   $235.60   $235.60  
  Purchase #5 $141.59   12.663%   $159.5195   $159.52   $159.50   $159.50  
  Purchase #6 $97.91   10.430%   $108.122   $108.12   $108.10   $108.10  
  Purchase #7 $22.29   7.860%   $24.042   $24.04   $24.05   $24.00  
  7 purchase totals = $897.99       $995.0954   $995.09   $995.10   $995.00