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 $57.36   6.770%   $61.2433   $61.24   $61.25   $61.20  
  Purchase #2 $207.75   8.499%   $225.4067   $225.41   $225.40   $225.40  
  Purchase #3 $190.98   13.372%   $216.5178   $216.52   $216.50   $216.50  
  Purchase #4 $94.39   7.381%   $101.3569   $101.36   $101.35   $101.40  
  Purchase #5 $34.66   6.502%   $36.9136   $36.91   $36.90   $36.90  
  Purchase #6 $120.44   6.259%   $127.9783   $127.98   $128.00   $128.00  
  Purchase #7 $22.90   6.366%   $24.3578   $24.36   $24.35   $24.40  
  7 purchase totals = $728.48       $793.7744   $793.78   $793.75   $793.80