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 $46.97   10.497%   $51.9004   $51.90   $51.90   $51.90  
  Purchase #2 $116.90   11.404%   $130.2313   $130.23   $130.25   $130.20  
  Purchase #3 $156.74   6.531%   $166.9767   $166.98   $167.00   $167.00  
  Purchase #4 $245.58   5.422%   $258.8953   $258.90   $258.90   $258.90  
  Purchase #5 $79.74   11.548%   $88.9484   $88.95   $88.95   $88.90  
  Purchase #6 $244.85   10.107%   $269.597   $269.60   $269.60   $269.60  
  Purchase #7 $181.59   4.133%   $189.0951   $189.10   $189.10   $189.10  
  7 purchase totals = $1,072.37       $1,155.6442   $1,155.66   $1,155.70   $1,155.60