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 $59.86   11.702%   $66.8648   $66.86   $66.85   $66.90  
  Purchase #2 $189.95   5.711%   $200.798   $200.80   $200.80   $200.80  
  Purchase #3 $66.91   10.521%   $73.9496   $73.95   $73.95   $73.90  
  Purchase #4 $129.48   12.506%   $145.6728   $145.67   $145.65   $145.70  
  Purchase #5 $232.59   8.507%   $252.3764   $252.38   $252.40   $252.40  
  Purchase #6 $97.49   6.188%   $103.5227   $103.52   $103.50   $103.50  
  Purchase #7 $77.87   12.409%   $87.5329   $87.53   $87.55   $87.50  
  7 purchase totals = $854.15       $930.7172   $930.71   $930.70   $930.70