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 $202.40   7.579%   $217.7399   $217.74   $217.75   $217.70  
  Purchase #2 $246.97   13.628%   $280.6271   $280.63   $280.65   $280.60  
  Purchase #3 $210.42   12.770%   $237.2906   $237.29   $237.30   $237.30  
  Purchase #4 $178.35   7.150%   $191.102   $191.10   $191.10   $191.10  
  Purchase #5 $49.95   5.813%   $52.8536   $52.85   $52.85   $52.90  
  Purchase #6 $136.75   11.230%   $152.107   $152.11   $152.10   $152.10  
  Purchase #7 $53.78   11.527%   $59.9792   $59.98   $60.00   $60.00  
  7 purchase totals = $1,078.62       $1,191.6994   $1,191.70   $1,191.75   $1,191.70