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 $244.77   12.471%   $275.2953   $275.30   $275.30   $275.30  
  Purchase #2 $95.53   11.421%   $106.4405   $106.44   $106.45   $106.40  
  Purchase #3 $228.33   12.736%   $257.4101   $257.41   $257.40   $257.40  
  Purchase #4 $22.49   9.627%   $24.6551   $24.66   $24.65   $24.70  
  Purchase #5 $224.86   4.720%   $235.4734   $235.47   $235.45   $235.50  
  Purchase #6 $58.56   8.742%   $63.6793   $63.68   $63.70   $63.70  
  Purchase #7 $194.31   5.313%   $204.6337   $204.63   $204.65   $204.60  
  7 purchase totals = $1,068.85       $1,167.5874   $1,167.59   $1,167.60   $1,167.60