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 $229.60   7.704%   $247.2884   $247.29   $247.30   $247.30  
  Purchase #2 $169.84   12.666%   $191.3519   $191.35   $191.35   $191.40  
  Purchase #3 $83.72   7.143%   $89.7001   $89.70   $89.70   $89.70  
  Purchase #4 $91.74   5.535%   $96.8178   $96.82   $96.80   $96.80  
  Purchase #5 $216.66   11.556%   $241.6972   $241.70   $241.70   $241.70  
  Purchase #6 $248.40   4.160%   $258.7334   $258.73   $258.75   $258.70  
  Purchase #7 $32.59   3.607%   $33.7655   $33.77   $33.75   $33.80  
  7 purchase totals = $1,072.55       $1,159.3543   $1,159.36   $1,159.35   $1,159.40