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 $223.70   8.587%   $242.9091   $242.91   $242.90   $242.90  
  Purchase #2 $19.43   13.413%   $22.0361   $22.04   $22.05   $22.00  
  Purchase #3 $118.65   8.614%   $128.8705   $128.87   $128.85   $128.90  
  Purchase #4 $132.69   4.281%   $138.3705   $138.37   $138.35   $138.40  
  Purchase #5 $48.44   11.839%   $54.1748   $54.17   $54.15   $54.20  
  Purchase #6 $202.80   13.637%   $230.4558   $230.46   $230.45   $230.50  
  Purchase #7 $223.76   11.790%   $250.1413   $250.14   $250.15   $250.10  
  7 purchase totals = $969.47       $1,066.9581   $1,066.96   $1,066.90   $1,067.00