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 $151.75   9.141%   $165.6215   $165.62   $165.60   $165.60  
  Purchase #2 $35.53   3.699%   $36.8443   $36.84   $36.85   $36.80  
  Purchase #3 $186.81   9.247%   $204.0843   $204.08   $204.10   $204.10  
  Purchase #4 $202.79   3.152%   $209.1819   $209.18   $209.20   $209.20  
  Purchase #5 $115.73   9.275%   $126.464   $126.46   $126.45   $126.50  
  Purchase #6 $112.54   12.305%   $126.388   $126.39   $126.40   $126.40  
  Purchase #7 $221.45   6.810%   $236.5307   $236.53   $236.55   $236.50  
  7 purchase totals = $1,026.60       $1,105.1147   $1,105.10   $1,105.15   $1,105.10