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 $90.60   5.446%   $95.5341   $95.53   $95.55   $95.50  
  Purchase #2 $229.80   4.366%   $239.8331   $239.83   $239.85   $239.80  
  Purchase #3 $53.61   13.122%   $60.6447   $60.64   $60.65   $60.60  
  Purchase #4 $143.53   6.317%   $152.5968   $152.60   $152.60   $152.60  
  Purchase #5 $152.55   11.111%   $169.4998   $169.50   $169.50   $169.50  
  Purchase #6 $58.65   6.399%   $62.403   $62.40   $62.40   $62.40  
  Purchase #7 $140.61   4.762%   $147.3058   $147.31   $147.30   $147.30  
  7 purchase totals = $869.35       $927.8173   $927.81   $927.85   $927.70