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 $205.93   10.722%   $228.0098   $228.01   $228.00   $228.00  
  Purchase #2 $191.88   12.386%   $215.6463   $215.65   $215.65   $215.60  
  Purchase #3 $5.70   4.121%   $5.9349   $5.93   $5.95   $5.90  
  Purchase #4 $238.78   9.515%   $261.4999   $261.50   $261.50   $261.50  
  Purchase #5 $211.65   7.622%   $227.782   $227.78   $227.80   $227.80  
  Purchase #6 $208.58   12.735%   $235.1427   $235.14   $235.15   $235.10  
  Purchase #7 $89.93   11.850%   $100.5867   $100.59   $100.60   $100.60  
  7 purchase totals = $1,152.45       $1,274.6023   $1,274.60   $1,274.65   $1,274.50