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 $65.88   13.137%   $74.5347   $74.53   $74.55   $74.50  
  Purchase #2 $238.86   12.637%   $269.0447   $269.04   $269.05   $269.00  
  Purchase #3 $214.52   9.780%   $235.5001   $235.50   $235.50   $235.50  
  Purchase #4 $83.68   13.538%   $95.0086   $95.01   $95.00   $95.00  
  Purchase #5 $113.67   5.252%   $119.6399   $119.64   $119.65   $119.60  
  Purchase #6 $117.73   7.749%   $126.8529   $126.85   $126.85   $126.90  
  Purchase #7 $249.32   8.583%   $270.7191   $270.72   $270.70   $270.70  
  7 purchase totals = $1,083.66       $1,191.3000   $1,191.29   $1,191.30   $1,191.20