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 $126.55   12.132%   $141.903   $141.90   $141.90   $141.90  
  Purchase #2 $211.98   3.532%   $219.4671   $219.47   $219.45   $219.50  
  Purchase #3 $82.98   7.290%   $89.0292   $89.03   $89.05   $89.00  
  Purchase #4 $157.58   9.720%   $172.8968   $172.90   $172.90   $172.90  
  Purchase #5 $235.73   5.690%   $249.143   $249.14   $249.15   $249.10  
  Purchase #6 $191.42   5.575%   $202.0917   $202.09   $202.10   $202.10  
  Purchase #7 $153.48   10.637%   $169.8057   $169.81   $169.80   $169.80  
  7 purchase totals = $1,159.72       $1,244.3365   $1,244.34   $1,244.35   $1,244.30