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 $229.85   10.206%   $253.3085   $253.31   $253.30   $253.30  
  Purchase #2 $51.61   8.130%   $55.8059   $55.81   $55.80   $55.80  
  Purchase #3 $245.53   9.719%   $269.3931   $269.39   $269.40   $269.40  
  Purchase #4 $103.53   6.254%   $110.0048   $110.00   $110.00   $110.00  
  Purchase #5 $182.41   12.452%   $205.1237   $205.12   $205.10   $205.10  
  Purchase #6 $181.43   6.350%   $192.9508   $192.95   $192.95   $193.00  
  Purchase #7 $24.25   13.182%   $27.4466   $27.45   $27.45   $27.40  
  7 purchase totals = $1,018.61       $1,114.0334   $1,114.03   $1,114.00   $1,114.00