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 $85.28   3.819%   $88.5368   $88.54   $88.55   $88.50  
  Purchase #2 $171.79   12.505%   $193.2723   $193.27   $193.25   $193.30  
  Purchase #3 $59.72   10.823%   $66.1835   $66.18   $66.20   $66.20  
  Purchase #4 $218.64   6.417%   $232.6701   $232.67   $232.65   $232.70  
  Purchase #5 $203.43   8.177%   $220.0645   $220.06   $220.05   $220.10  
  Purchase #6 $94.73   6.725%   $101.1006   $101.10   $101.10   $101.10  
  Purchase #7 $146.89   4.213%   $153.0785   $153.08   $153.10   $153.10  
  7 purchase totals = $980.48       $1,054.9063   $1,054.90   $1,054.90   $1,055.00