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 $197.57   6.796%   $210.9969   $211.00   $211.00   $211.00  
  Purchase #2 $227.94   8.390%   $247.0642   $247.06   $247.05   $247.10  
  Purchase #3 $114.44   8.746%   $124.4489   $124.45   $124.45   $124.40  
  Purchase #4 $209.29   9.820%   $229.8423   $229.84   $229.85   $229.80  
  Purchase #5 $119.38   6.410%   $127.0323   $127.03   $127.05   $127.00  
  Purchase #6 $119.86   3.291%   $123.8046   $123.80   $123.80   $123.80  
  Purchase #7 $217.56   6.463%   $231.6209   $231.62   $231.60   $231.60  
  7 purchase totals = $1,206.04       $1,294.8101   $1,294.80   $1,294.80   $1,294.70