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 $218.29   8.676%   $237.2288   $237.23   $237.25   $237.20  
  Purchase #2 $155.53   10.818%   $172.3552   $172.36   $172.35   $172.40  
  Purchase #3 $125.85   9.474%   $137.773   $137.77   $137.75   $137.80  
  Purchase #4 $55.39   8.855%   $60.2948   $60.29   $60.30   $60.30  
  Purchase #5 $63.74   8.575%   $69.2057   $69.21   $69.20   $69.20  
  Purchase #6 $232.35   12.280%   $260.8826   $260.88   $260.90   $260.90  
  Purchase #7 $175.25   9.544%   $191.9759   $191.98   $192.00   $192.00  
  7 purchase totals = $1,026.40       $1,129.7160   $1,129.72   $1,129.75   $1,129.80