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 $125.91   12.751%   $141.9648   $141.96   $141.95   $142.00  
  Purchase #2 $93.83   6.500%   $99.929   $99.93   $99.95   $99.90  
  Purchase #3 $247.70   10.187%   $272.9332   $272.93   $272.95   $272.90  
  Purchase #4 $86.59   9.865%   $95.1321   $95.13   $95.15   $95.10  
  Purchase #5 $85.46   10.855%   $94.7367   $94.74   $94.75   $94.70  
  Purchase #6 $230.92   6.549%   $246.043   $246.04   $246.05   $246.00  
  Purchase #7 $190.83   7.701%   $205.5258   $205.53   $205.55   $205.50  
  7 purchase totals = $1,061.24       $1,156.2646   $1,156.26   $1,156.35   $1,156.10