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 $57.98   9.154%   $63.2875   $63.29   $63.30   $63.30  
  Purchase #2 $237.38   10.235%   $261.6758   $261.68   $261.70   $261.70  
  Purchase #3 $160.27   13.204%   $181.4321   $181.43   $181.45   $181.40  
  Purchase #4 $87.55   6.316%   $93.0797   $93.08   $93.10   $93.10  
  Purchase #5 $229.76   11.627%   $256.4742   $256.47   $256.45   $256.50  
  Purchase #6 $160.84   5.834%   $170.2234   $170.22   $170.20   $170.20  
  Purchase #7 $200.96   12.305%   $225.6881   $225.69   $225.70   $225.70  
  7 purchase totals = $1,134.74       $1,251.8608   $1,251.86   $1,251.90   $1,251.90