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 $34.39   8.522%   $37.3207   $37.32   $37.30   $37.30  
  Purchase #2 $182.79   11.586%   $203.968   $203.97   $203.95   $204.00  
  Purchase #3 $241.82   9.837%   $265.6078   $265.61   $265.60   $265.60  
  Purchase #4 $188.39   12.550%   $212.0329   $212.03   $212.05   $212.00  
  Purchase #5 $237.42   8.514%   $257.6339   $257.63   $257.65   $257.60  
  Purchase #6 $128.82   6.620%   $137.3479   $137.35   $137.35   $137.30  
  Purchase #7 $103.93   8.752%   $113.026   $113.03   $113.05   $113.00  
  7 purchase totals = $1,117.56       $1,226.9372   $1,226.94   $1,226.95   $1,226.80