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 $53.92   9.198%   $58.8796   $58.88   $58.90   $58.90  
  Purchase #2 $186.75   10.659%   $206.6557   $206.66   $206.65   $206.70  
  Purchase #3 $145.62   9.351%   $159.2369   $159.24   $159.25   $159.20  
  Purchase #4 $17.78   8.203%   $19.2385   $19.24   $19.25   $19.20  
  Purchase #5 $106.50   5.701%   $112.5716   $112.57   $112.55   $112.60  
  Purchase #6 $52.51   11.159%   $58.3696   $58.37   $58.35   $58.40  
  Purchase #7 $139.32   9.159%   $152.0803   $152.08   $152.10   $152.10  
  7 purchase totals = $702.40       $767.0322   $767.04   $767.05   $767.10