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 $241.51   5.552%   $254.9186   $254.92   $254.90   $254.90  
  Purchase #2 $102.33   6.580%   $109.0633   $109.06   $109.05   $109.10  
  Purchase #3 $58.29   6.418%   $62.0311   $62.03   $62.05   $62.00  
  Purchase #4 $85.39   6.251%   $90.7277   $90.73   $90.75   $90.70  
  Purchase #5 $7.56   11.326%   $8.4162   $8.42   $8.40   $8.40  
  Purchase #6 $213.75   11.308%   $237.9209   $237.92   $237.90   $237.90  
  Purchase #7 $244.78   5.293%   $257.7362   $257.74   $257.75   $257.70  
  7 purchase totals = $953.61       $1,020.8140   $1,020.82   $1,020.80   $1,020.70