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 $48.43   11.538%   $54.0179   $54.02   $54.00   $54.00  
  Purchase #2 $152.83   13.334%   $173.2084   $173.21   $173.20   $173.20  
  Purchase #3 $12.74   12.864%   $14.3789   $14.38   $14.40   $14.40  
  Purchase #4 $238.66   3.350%   $246.6551   $246.66   $246.65   $246.70  
  Purchase #5 $126.68   10.822%   $140.3893   $140.39   $140.40   $140.40  
  Purchase #6 $166.25   4.737%   $174.1253   $174.13   $174.15   $174.10  
  Purchase #7 $231.96   12.325%   $260.5491   $260.55   $260.55   $260.50  
  7 purchase totals = $977.55       $1,063.3240   $1,063.34   $1,063.35   $1,063.30