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 $204.62   3.604%   $211.9945   $211.99   $212.00   $212.00  
  Purchase #2 $194.43   9.196%   $212.3098   $212.31   $212.30   $212.30  
  Purchase #3 $59.65   6.580%   $63.575   $63.58   $63.60   $63.60  
  Purchase #4 $133.34   5.304%   $140.4124   $140.41   $140.40   $140.40  
  Purchase #5 $62.43   3.620%   $64.69   $64.69   $64.70   $64.70  
  Purchase #6 $215.38   8.393%   $233.4568   $233.46   $233.45   $233.50  
  Purchase #7 $79.48   11.300%   $88.4612   $88.46   $88.45   $88.50  
  7 purchase totals = $949.33       $1,014.8997   $1,014.90   $1,014.90   $1,015.00