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 $54.82   12.642%   $61.7503   $61.75   $61.75   $61.80  
  Purchase #2 $195.99   12.529%   $220.5456   $220.55   $220.55   $220.50  
  Purchase #3 $103.98   4.816%   $108.9877   $108.99   $109.00   $109.00  
  Purchase #4 $182.42   12.840%   $205.8427   $205.84   $205.85   $205.80  
  Purchase #5 $241.84   8.531%   $262.4714   $262.47   $262.45   $262.50  
  Purchase #6 $83.77   4.154%   $87.2498   $87.25   $87.25   $87.20  
  Purchase #7 $26.93   10.331%   $29.7121   $29.71   $29.70   $29.70  
  7 purchase totals = $889.75       $976.5596   $976.56   $976.55   $976.50