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 $69.84   6.210%   $74.1771   $74.18   $74.20   $74.20  
  Purchase #2 $233.45   5.391%   $246.0353   $246.04   $246.05   $246.00  
  Purchase #3 $136.67   9.197%   $149.2395   $149.24   $149.25   $149.20  
  Purchase #4 $82.95   5.752%   $87.7213   $87.72   $87.70   $87.70  
  Purchase #5 $208.94   3.653%   $216.5726   $216.57   $216.55   $216.60  
  Purchase #6 $217.65   8.516%   $236.1851   $236.19   $236.20   $236.20  
  Purchase #7 $140.95   6.332%   $149.875   $149.88   $149.90   $149.90  
  7 purchase totals = $1,090.45       $1,159.8059   $1,159.82   $1,159.85   $1,159.80