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 $64.45   13.818%   $73.3557   $73.36   $73.35   $73.40  
  Purchase #2 $193.53   13.656%   $219.9585   $219.96   $219.95   $220.00  
  Purchase #3 $185.98   7.135%   $199.2497   $199.25   $199.25   $199.20  
  Purchase #4 $212.70   6.629%   $226.7999   $226.80   $226.80   $226.80  
  Purchase #5 $167.39   13.227%   $189.5307   $189.53   $189.55   $189.50  
  Purchase #6 $124.97   9.242%   $136.5197   $136.52   $136.50   $136.50  
  Purchase #7 $197.41   5.394%   $208.0583   $208.06   $208.05   $208.10  
  7 purchase totals = $1,146.43       $1,253.4725   $1,253.48   $1,253.45   $1,253.50