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 $45.25   5.180%   $47.594   $47.59   $47.60   $47.60  
  Purchase #2 $94.37   11.633%   $105.3481   $105.35   $105.35   $105.30  
  Purchase #3 $26.56   6.457%   $28.275   $28.28   $28.30   $28.30  
  Purchase #4 $81.87   3.726%   $84.9205   $84.92   $84.90   $84.90  
  Purchase #5 $139.30   7.651%   $149.9578   $149.96   $149.95   $150.00  
  Purchase #6 $151.91   13.219%   $171.991   $171.99   $172.00   $172.00  
  Purchase #7 $161.65   12.157%   $181.3018   $181.30   $181.30   $181.30  
  7 purchase totals = $700.91       $769.3882   $769.39   $769.40   $769.40