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 $46.49   11.828%   $51.9888   $51.99   $52.00   $52.00  
  Purchase #2 $209.75   8.365%   $227.2956   $227.30   $227.30   $227.30  
  Purchase #3 $203.44   9.317%   $222.3945   $222.39   $222.40   $222.40  
  Purchase #4 $246.60   5.831%   $260.9792   $260.98   $261.00   $261.00  
  Purchase #5 $99.30   8.685%   $107.9242   $107.92   $107.90   $107.90  
  Purchase #6 $152.65   6.677%   $162.8424   $162.84   $162.85   $162.80  
  Purchase #7 $19.84   12.648%   $22.3494   $22.35   $22.35   $22.30  
  7 purchase totals = $978.07       $1,055.7741   $1,055.77   $1,055.80   $1,055.70