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 $67.27   10.119%   $74.0771   $74.08   $74.10   $74.10  
  Purchase #2 $135.45   13.144%   $153.2535   $153.25   $153.25   $153.30  
  Purchase #3 $210.93   12.202%   $236.6677   $236.67   $236.65   $236.70  
  Purchase #4 $55.29   13.538%   $62.7752   $62.78   $62.80   $62.80  
  Purchase #5 $118.33   10.251%   $130.46   $130.46   $130.45   $130.50  
  Purchase #6 $146.88   6.142%   $155.9014   $155.90   $155.90   $155.90  
  Purchase #7 $170.97   9.771%   $187.6755   $187.68   $187.70   $187.70  
  7 purchase totals = $905.12       $1,000.8104   $1,000.82   $1,000.85   $1,001.00