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 $140.75   12.516%   $158.3663   $158.37   $158.35   $158.40  
  Purchase #2 $10.49   9.415%   $11.4776   $11.48   $11.50   $11.50  
  Purchase #3 $247.75   3.464%   $256.3321   $256.33   $256.35   $256.30  
  Purchase #4 $184.34   9.109%   $201.1315   $201.13   $201.15   $201.10  
  Purchase #5 $197.97   3.557%   $205.0118   $205.01   $205.00   $205.00  
  Purchase #6 $231.72   13.796%   $263.6881   $263.69   $263.70   $263.70  
  Purchase #7 $231.37   5.412%   $243.8917   $243.89   $243.90   $243.90  
  7 purchase totals = $1,244.39       $1,339.8991   $1,339.90   $1,339.95   $1,339.90