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 $66.56   7.738%   $71.7104   $71.71   $71.70   $71.70  
  Purchase #2 $104.71   13.328%   $118.6657   $118.67   $118.65   $118.70  
  Purchase #3 $22.43   13.362%   $25.4271   $25.43   $25.45   $25.40  
  Purchase #4 $207.37   13.380%   $235.1161   $235.12   $235.10   $235.10  
  Purchase #5 $247.45   10.240%   $272.7889   $272.79   $272.80   $272.80  
  Purchase #6 $118.61   3.535%   $122.8029   $122.80   $122.80   $122.80  
  Purchase #7 $207.75   3.129%   $214.2505   $214.25   $214.25   $214.30  
  7 purchase totals = $974.88       $1,060.7616   $1,060.77   $1,060.75   $1,060.80