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 $186.42   9.304%   $203.7645   $203.76   $203.75   $203.80  
  Purchase #2 $242.31   7.280%   $259.9502   $259.95   $259.95   $260.00  
  Purchase #3 $6.27   9.474%   $6.864   $6.86   $6.85   $6.90  
  Purchase #4 $21.41   12.545%   $24.0959   $24.10   $24.10   $24.10  
  Purchase #5 $128.60   13.402%   $145.835   $145.84   $145.85   $145.80  
  Purchase #6 $195.51   8.494%   $212.1166   $212.12   $212.10   $212.10  
  Purchase #7 $69.45   4.373%   $72.487   $72.49   $72.50   $72.50  
  7 purchase totals = $849.97       $925.1132   $925.12   $925.10   $925.20