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 $57.86   12.702%   $65.2094   $65.21   $65.20   $65.20  
  Purchase #2 $58.55   3.372%   $60.5243   $60.52   $60.50   $60.50  
  Purchase #3 $24.47   12.663%   $27.5686   $27.57   $27.55   $27.60  
  Purchase #4 $110.79   5.243%   $116.5987   $116.60   $116.60   $116.60  
  Purchase #5 $189.84   8.764%   $206.4776   $206.48   $206.50   $206.50  
  Purchase #6 $184.40   8.615%   $200.2861   $200.29   $200.30   $200.30  
  Purchase #7 $241.71   3.757%   $250.791   $250.79   $250.80   $250.80  
  7 purchase totals = $867.62       $927.4557   $927.46   $927.45   $927.50