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 $186.62   10.746%   $206.6742   $206.67   $206.65   $206.70  
  Purchase #2 $36.33   12.719%   $40.9508   $40.95   $40.95   $41.00  
  Purchase #3 $232.93   10.556%   $257.5181   $257.52   $257.50   $257.50  
  Purchase #4 $179.27   13.773%   $203.9609   $203.96   $203.95   $204.00  
  Purchase #5 $62.49   7.334%   $67.073   $67.07   $67.05   $67.10  
  Purchase #6 $94.30   8.116%   $101.9534   $101.95   $101.95   $102.00  
  Purchase #7 $229.93   4.844%   $241.0678   $241.07   $241.05   $241.10  
  7 purchase totals = $1,021.87       $1,119.1982   $1,119.19   $1,119.10   $1,119.40