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 $206.84   5.153%   $217.4985   $217.50   $217.50   $217.50  
  Purchase #2 $39.89   13.368%   $45.2225   $45.22   $45.20   $45.20  
  Purchase #3 $210.79   7.790%   $227.2105   $227.21   $227.20   $227.20  
  Purchase #4 $99.69   4.299%   $103.9757   $103.98   $104.00   $104.00  
  Purchase #5 $151.85   12.563%   $170.9269   $170.93   $170.95   $170.90  
  Purchase #6 $218.68   5.656%   $231.0485   $231.05   $231.05   $231.00  
  Purchase #7 $162.87   11.323%   $181.3118   $181.31   $181.30   $181.30  
  7 purchase totals = $1,090.61       $1,177.1944   $1,177.20   $1,177.20   $1,177.10