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 $230.98   8.784%   $251.2693   $251.27   $251.25   $251.30  
  Purchase #2 $96.71   9.400%   $105.8007   $105.80   $105.80   $105.80  
  Purchase #3 $145.61   7.754%   $156.9006   $156.90   $156.90   $156.90  
  Purchase #4 $193.78   4.516%   $202.5311   $202.53   $202.55   $202.50  
  Purchase #5 $75.41   10.397%   $83.2504   $83.25   $83.25   $83.30  
  Purchase #6 $247.27   11.289%   $275.1843   $275.18   $275.20   $275.20  
  Purchase #7 $17.52   6.299%   $18.6236   $18.62   $18.60   $18.60  
  7 purchase totals = $1,007.28       $1,093.5600   $1,093.55   $1,093.55   $1,093.60