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 $73.32   13.274%   $83.0525   $83.05   $83.05   $83.10  
  Purchase #2 $248.34   11.179%   $276.1019   $276.10   $276.10   $276.10  
  Purchase #3 $58.40   12.829%   $65.8921   $65.89   $65.90   $65.90  
  Purchase #4 $179.26   8.164%   $193.8948   $193.89   $193.90   $193.90  
  Purchase #5 $83.72   3.862%   $86.9533   $86.95   $86.95   $87.00  
  Purchase #6 $244.67   3.392%   $252.9692   $252.97   $252.95   $253.00  
  Purchase #7 $236.99   6.753%   $252.9939   $252.99   $253.00   $253.00  
  7 purchase totals = $1,124.70       $1,211.8577   $1,211.84   $1,211.85   $1,212.00