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 $216.33   11.842%   $241.9478   $241.95   $241.95   $241.90  
  Purchase #2 $23.68   12.433%   $26.6241   $26.62   $26.60   $26.60  
  Purchase #3 $204.34   4.247%   $213.0183   $213.02   $213.00   $213.00  
  Purchase #4 $142.27   7.272%   $152.6159   $152.62   $152.60   $152.60  
  Purchase #5 $98.29   7.868%   $106.0235   $106.02   $106.00   $106.00  
  Purchase #6 $174.30   11.468%   $194.2887   $194.29   $194.30   $194.30  
  Purchase #7 $121.90   3.870%   $126.6175   $126.62   $126.60   $126.60  
  7 purchase totals = $981.11       $1,061.1358   $1,061.14   $1,061.05   $1,061.00