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 $59.78   5.319%   $62.9597   $62.96   $62.95   $63.00  
  Purchase #2 $16.66   3.316%   $17.2124   $17.21   $17.20   $17.20  
  Purchase #3 $147.25   4.608%   $154.0353   $154.04   $154.05   $154.00  
  Purchase #4 $243.70   10.842%   $270.122   $270.12   $270.10   $270.10  
  Purchase #5 $64.62   6.772%   $68.9961   $69.00   $69.00   $69.00  
  Purchase #6 $148.29   13.196%   $167.8583   $167.86   $167.85   $167.90  
  Purchase #7 $179.41   11.870%   $200.706   $200.71   $200.70   $200.70  
  7 purchase totals = $859.71       $941.8898   $941.90   $941.85   $941.90