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 $22.54   7.507%   $24.2321   $24.23   $24.25   $24.20  
  Purchase #2 $181.67   13.248%   $205.7376   $205.74   $205.75   $205.70  
  Purchase #3 $93.67   7.633%   $100.8198   $100.82   $100.80   $100.80  
  Purchase #4 $60.54   3.850%   $62.8708   $62.87   $62.85   $62.90  
  Purchase #5 $53.79   5.735%   $56.8749   $56.87   $56.85   $56.90  
  Purchase #6 $216.33   4.798%   $226.7095   $226.71   $226.70   $226.70  
  Purchase #7 $58.32   4.406%   $60.8896   $60.89   $60.90   $60.90  
  7 purchase totals = $686.86       $738.1343   $738.13   $738.10   $738.10