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 $225.76   4.859%   $236.7297   $236.73   $236.75   $236.70  
  Purchase #2 $39.37   6.459%   $41.9129   $41.91   $41.90   $41.90  
  Purchase #3 $55.74   12.803%   $62.8764   $62.88   $62.90   $62.90  
  Purchase #4 $171.76   11.774%   $191.983   $191.98   $192.00   $192.00  
  Purchase #5 $56.67   7.826%   $61.105   $61.11   $61.10   $61.10  
  Purchase #6 $172.61   4.840%   $180.9643   $180.96   $180.95   $181.00  
  Purchase #7 $116.98   13.851%   $133.1829   $133.18   $133.20   $133.20  
  7 purchase totals = $838.89       $908.7542   $908.75   $908.80   $908.80