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 $46.87   10.393%   $51.7412   $51.74   $51.75   $51.70  
  Purchase #2 $208.32   12.184%   $233.7017   $233.70   $233.70   $233.70  
  Purchase #3 $22.67   4.801%   $23.7584   $23.76   $23.75   $23.80  
  Purchase #4 $137.89   9.164%   $150.5262   $150.53   $150.55   $150.50  
  Purchase #5 $151.92   9.525%   $166.3904   $166.39   $166.40   $166.40  
  Purchase #6 $156.41   13.209%   $177.0702   $177.07   $177.05   $177.10  
  Purchase #7 $197.66   7.316%   $212.1208   $212.12   $212.10   $212.10  
  7 purchase totals = $921.74       $1,015.3089   $1,015.31   $1,015.30   $1,015.30