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 $163.91   8.191%   $177.3359   $177.34   $177.35   $177.30  
  Purchase #2 $54.87   12.414%   $61.6816   $61.68   $61.70   $61.70  
  Purchase #3 $194.49   4.838%   $203.8994   $203.90   $203.90   $203.90  
  Purchase #4 $25.98   5.253%   $27.3447   $27.34   $27.35   $27.30  
  Purchase #5 $218.29   12.292%   $245.1222   $245.12   $245.10   $245.10  
  Purchase #6 $84.45   7.761%   $91.0042   $91.00   $91.00   $91.00  
  Purchase #7 $202.42   5.371%   $213.292   $213.29   $213.30   $213.30  
  7 purchase totals = $944.41       $1,019.6800   $1,019.67   $1,019.70   $1,019.60