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 $167.66   8.374%   $181.6998   $181.70   $181.70   $181.70  
  Purchase #2 $31.91   3.130%   $32.9088   $32.91   $32.90   $32.90  
  Purchase #3 $210.42   8.267%   $227.8154   $227.82   $227.80   $227.80  
  Purchase #4 $29.93   8.132%   $32.3639   $32.36   $32.35   $32.40  
  Purchase #5 $122.69   6.538%   $130.7115   $130.71   $130.70   $130.70  
  Purchase #6 $113.74   4.213%   $118.5319   $118.53   $118.55   $118.50  
  Purchase #7 $85.88   7.694%   $92.4876   $92.49   $92.50   $92.50  
  7 purchase totals = $762.23       $816.5189   $816.52   $816.50   $816.50