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 $141.31   8.774%   $153.7085   $153.71   $153.70   $153.70  
  Purchase #2 $122.62   10.807%   $135.8715   $135.87   $135.85   $135.90  
  Purchase #3 $37.62   7.226%   $40.3384   $40.34   $40.35   $40.30  
  Purchase #4 $238.28   12.385%   $267.791   $267.79   $267.80   $267.80  
  Purchase #5 $218.43   11.833%   $244.2768   $244.28   $244.30   $244.30  
  Purchase #6 $147.39   6.150%   $156.4545   $156.45   $156.45   $156.50  
  Purchase #7 $118.98   7.728%   $128.1748   $128.17   $128.15   $128.20  
  7 purchase totals = $1,024.63       $1,126.6155   $1,126.61   $1,126.60   $1,126.70