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 $56.34   5.110%   $59.219   $59.22   $59.20   $59.20  
  Purchase #2 $181.73   10.565%   $200.9298   $200.93   $200.95   $200.90  
  Purchase #3 $199.39   8.759%   $216.8546   $216.85   $216.85   $216.90  
  Purchase #4 $113.93   13.474%   $129.2809   $129.28   $129.30   $129.30  
  Purchase #5 $16.65   8.258%   $18.025   $18.03   $18.05   $18.00  
  Purchase #6 $71.66   11.109%   $79.6207   $79.62   $79.60   $79.60  
  Purchase #7 $57.59   13.352%   $65.2794   $65.28   $65.30   $65.30  
  7 purchase totals = $697.29       $769.2094   $769.21   $769.25   $769.20