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 $246.32   6.374%   $262.0204   $262.02   $262.00   $262.00  
  Purchase #2 $182.95   12.247%   $205.3559   $205.36   $205.35   $205.40  
  Purchase #3 $75.37   12.728%   $84.9631   $84.96   $84.95   $85.00  
  Purchase #4 $214.98   3.282%   $222.0356   $222.04   $222.05   $222.00  
  Purchase #5 $160.84   12.123%   $180.3386   $180.34   $180.35   $180.30  
  Purchase #6 $155.58   7.456%   $167.18   $167.18   $167.20   $167.20  
  Purchase #7 $124.72   10.410%   $137.7034   $137.70   $137.70   $137.70  
  7 purchase totals = $1,160.76       $1,259.5970   $1,259.60   $1,259.60   $1,259.60