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 $74.99   4.816%   $78.6015   $78.60   $78.60   $78.60  
  Purchase #2 $145.84   3.555%   $151.0246   $151.02   $151.00   $151.00  
  Purchase #3 $218.56   12.843%   $246.6297   $246.63   $246.65   $246.60  
  Purchase #4 $203.45   7.425%   $218.5562   $218.56   $218.55   $218.60  
  Purchase #5 $236.88   8.161%   $256.2118   $256.21   $256.20   $256.20  
  Purchase #6 $131.96   4.678%   $138.1331   $138.13   $138.15   $138.10  
  Purchase #7 $111.87   3.469%   $115.7508   $115.75   $115.75   $115.80  
  7 purchase totals = $1,123.55       $1,204.9077   $1,204.90   $1,204.90   $1,204.90