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 $238.72   3.306%   $246.6121   $246.61   $246.60   $246.60  
  Purchase #2 $230.54   11.266%   $256.5126   $256.51   $256.50   $256.50  
  Purchase #3 $29.39   5.489%   $31.0032   $31.00   $31.00   $31.00  
  Purchase #4 $72.58   6.261%   $77.1242   $77.12   $77.10   $77.10  
  Purchase #5 $211.63   11.565%   $236.105   $236.11   $236.10   $236.10  
  Purchase #6 $57.89   3.869%   $60.1298   $60.13   $60.15   $60.10  
  Purchase #7 $119.94   4.232%   $125.0159   $125.02   $125.00   $125.00  
  7 purchase totals = $960.69       $1,032.5028   $1,032.50   $1,032.45   $1,032.40