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 $51.62   8.798%   $56.1615   $56.16   $56.15   $56.20  
  Purchase #2 $53.59   12.574%   $60.3284   $60.33   $60.35   $60.30  
  Purchase #3 $77.93   11.695%   $87.0439   $87.04   $87.05   $87.00  
  Purchase #4 $182.42   8.645%   $198.1902   $198.19   $198.20   $198.20  
  Purchase #5 $119.55   9.740%   $131.1942   $131.19   $131.20   $131.20  
  Purchase #6 $209.94   9.221%   $229.2986   $229.30   $229.30   $229.30  
  Purchase #7 $125.93   12.256%   $141.364   $141.36   $141.35   $141.40  
  7 purchase totals = $820.98       $903.5808   $903.57   $903.60   $903.60