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 $212.26   10.832%   $235.252   $235.25   $235.25   $235.30  
  Purchase #2 $61.57   13.278%   $69.7453   $69.75   $69.75   $69.70  
  Purchase #3 $50.85   13.653%   $57.7926   $57.79   $57.80   $57.80  
  Purchase #4 $69.62   5.572%   $73.4992   $73.50   $73.50   $73.50  
  Purchase #5 $126.56   9.473%   $138.549   $138.55   $138.55   $138.50  
  Purchase #6 $103.42   5.366%   $108.9695   $108.97   $108.95   $109.00  
  Purchase #7 $229.35   12.726%   $258.5371   $258.54   $258.55   $258.50  
  7 purchase totals = $853.63       $942.3447   $942.35   $942.35   $942.30