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 $22.46   9.801%   $24.6613   $24.66   $24.65   $24.70  
  Purchase #2 $155.71   7.788%   $167.8367   $167.84   $167.85   $167.80  
  Purchase #3 $95.76   8.704%   $104.095   $104.10   $104.10   $104.10  
  Purchase #4 $205.93   10.482%   $227.5156   $227.52   $227.50   $227.50  
  Purchase #5 $96.73   6.609%   $103.1229   $103.12   $103.10   $103.10  
  Purchase #6 $210.56   4.320%   $219.6562   $219.66   $219.65   $219.70  
  Purchase #7 $191.90   11.180%   $213.3544   $213.35   $213.35   $213.40  
  7 purchase totals = $979.05       $1,060.2421   $1,060.25   $1,060.20   $1,060.30