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 $31.69   11.483%   $35.329   $35.33   $35.35   $35.30  
  Purchase #2 $136.41   12.374%   $153.2894   $153.29   $153.30   $153.30  
  Purchase #3 $204.39   6.113%   $216.8844   $216.88   $216.90   $216.90  
  Purchase #4 $102.57   4.239%   $106.9179   $106.92   $106.90   $106.90  
  Purchase #5 $216.93   9.830%   $238.2542   $238.25   $238.25   $238.30  
  Purchase #6 $17.50   7.213%   $18.7623   $18.76   $18.75   $18.80  
  Purchase #7 $71.77   6.617%   $76.519   $76.52   $76.50   $76.50  
  7 purchase totals = $781.26       $845.9562   $845.95   $845.95   $846.00