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 $61.70   11.346%   $68.7005   $68.70   $68.70   $68.70  
  Purchase #2 $105.46   8.217%   $114.1256   $114.13   $114.15   $114.10  
  Purchase #3 $18.66   12.506%   $20.9936   $20.99   $21.00   $21.00  
  Purchase #4 $212.98   10.192%   $234.6869   $234.69   $234.70   $234.70  
  Purchase #5 $199.79   7.707%   $215.1878   $215.19   $215.20   $215.20  
  Purchase #6 $192.89   9.809%   $211.8106   $211.81   $211.80   $211.80  
  Purchase #7 $5.52   11.555%   $6.1578   $6.16   $6.15   $6.20  
  7 purchase totals = $797.00       $871.6628   $871.67   $871.70   $871.70