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 $212.33   10.752%   $235.1597   $235.16   $235.15   $235.20  
  Purchase #2 $140.29   4.325%   $146.3575   $146.36   $146.35   $146.40  
  Purchase #3 $22.57   8.450%   $24.4772   $24.48   $24.50   $24.50  
  Purchase #4 $210.92   7.123%   $225.9438   $225.94   $225.95   $225.90  
  Purchase #5 $165.58   11.183%   $184.0968   $184.10   $184.10   $184.10  
  Purchase #6 $50.98   9.755%   $55.9531   $55.95   $55.95   $56.00  
  Purchase #7 $245.46   9.374%   $268.4694   $268.47   $268.45   $268.50  
  7 purchase totals = $1,048.13       $1,140.4575   $1,140.46   $1,140.45   $1,140.60