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 $62.50   9.565%   $68.4781   $68.48   $68.50   $68.50  
  Purchase #2 $188.45   6.426%   $200.5598   $200.56   $200.55   $200.60  
  Purchase #3 $110.39   7.476%   $118.6428   $118.64   $118.65   $118.60  
  Purchase #4 $100.95   5.285%   $106.2852   $106.29   $106.30   $106.30  
  Purchase #5 $140.81   8.707%   $153.0703   $153.07   $153.05   $153.10  
  Purchase #6 $229.40   12.385%   $257.8112   $257.81   $257.80   $257.80  
  Purchase #7 $105.33   12.537%   $118.5352   $118.54   $118.55   $118.50  
  7 purchase totals = $937.83       $1,023.3826   $1,023.39   $1,023.40   $1,023.40