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 $59.28   8.201%   $64.1416   $64.14   $64.15   $64.10  
  Purchase #2 $198.65   6.278%   $211.1212   $211.12   $211.10   $211.10  
  Purchase #3 $160.42   3.307%   $165.7251   $165.73   $165.75   $165.70  
  Purchase #4 $209.56   5.603%   $221.3016   $221.30   $221.30   $221.30  
  Purchase #5 $110.64   12.699%   $124.6902   $124.69   $124.70   $124.70  
  Purchase #6 $114.70   3.212%   $118.3842   $118.38   $118.40   $118.40  
  Purchase #7 $119.93   5.146%   $126.1016   $126.10   $126.10   $126.10  
  7 purchase totals = $973.18       $1,031.4655   $1,031.46   $1,031.50   $1,031.40