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 $211.34   10.434%   $233.3912   $233.39   $233.40   $233.40  
  Purchase #2 $53.83   7.242%   $57.7284   $57.73   $57.75   $57.70  
  Purchase #3 $162.62   13.148%   $184.0013   $184.00   $184.00   $184.00  
  Purchase #4 $56.31   12.672%   $63.4456   $63.45   $63.45   $63.40  
  Purchase #5 $194.59   13.172%   $220.2214   $220.22   $220.20   $220.20  
  Purchase #6 $146.86   10.104%   $161.6987   $161.70   $161.70   $161.70  
  Purchase #7 $172.56   10.254%   $190.2543   $190.25   $190.25   $190.30  
  7 purchase totals = $998.11       $1,110.7409   $1,110.74   $1,110.75   $1,110.70