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 $108.33   13.262%   $122.6967   $122.70   $122.70   $122.70  
  Purchase #2 $175.72   13.621%   $199.6548   $199.65   $199.65   $199.70  
  Purchase #3 $232.84   5.750%   $246.2283   $246.23   $246.25   $246.20  
  Purchase #4 $228.63   6.110%   $242.5993   $242.60   $242.60   $242.60  
  Purchase #5 $148.50   4.814%   $155.6488   $155.65   $155.65   $155.60  
  Purchase #6 $153.97   11.201%   $171.2162   $171.22   $171.20   $171.20  
  Purchase #7 $47.57   7.686%   $51.2262   $51.23   $51.25   $51.20  
  7 purchase totals = $1,095.56       $1,189.2703   $1,189.28   $1,189.30   $1,189.20