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 $85.85   5.285%   $90.3872   $90.39   $90.40   $90.40  
  Purchase #2 $66.44   10.316%   $73.294   $73.29   $73.30   $73.30  
  Purchase #3 $202.28   7.489%   $217.4287   $217.43   $217.45   $217.40  
  Purchase #4 $58.40   6.437%   $62.1592   $62.16   $62.15   $62.20  
  Purchase #5 $26.32   7.622%   $28.3261   $28.33   $28.35   $28.30  
  Purchase #6 $162.40   6.264%   $172.5727   $172.57   $172.55   $172.60  
  Purchase #7 $9.51   3.855%   $9.8766   $9.88   $9.90   $9.90  
  7 purchase totals = $611.20       $654.0445   $654.05   $654.10   $654.10