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 $69.74   11.167%   $77.5279   $77.53   $77.55   $77.50  
  Purchase #2 $101.67   10.439%   $112.2833   $112.28   $112.30   $112.30  
  Purchase #3 $80.81   8.462%   $87.6481   $87.65   $87.65   $87.60  
  Purchase #4 $217.61   6.855%   $232.5272   $232.53   $232.55   $232.50  
  Purchase #5 $61.94   10.581%   $68.4939   $68.49   $68.50   $68.50  
  Purchase #6 $225.67   12.603%   $254.1112   $254.11   $254.10   $254.10  
  Purchase #7 $240.46   13.464%   $272.8355   $272.84   $272.85   $272.80  
  7 purchase totals = $997.90       $1,105.4271   $1,105.43   $1,105.50   $1,105.30