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 $47.41   8.820%   $51.5916   $51.59   $51.60   $51.60  
  Purchase #2 $217.58   13.838%   $247.6887   $247.69   $247.70   $247.70  
  Purchase #3 $54.87   5.486%   $57.8802   $57.88   $57.90   $57.90  
  Purchase #4 $89.37   5.265%   $94.0753   $94.08   $94.10   $94.10  
  Purchase #5 $116.58   10.189%   $128.4583   $128.46   $128.45   $128.50  
  Purchase #6 $65.62   3.572%   $67.9639   $67.96   $67.95   $68.00  
  Purchase #7 $155.44   5.326%   $163.7187   $163.72   $163.70   $163.70  
  7 purchase totals = $746.87       $811.3767   $811.38   $811.40   $811.50