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 $88.85   8.503%   $96.4049   $96.40   $96.40   $96.40  
  Purchase #2 $219.75   9.453%   $240.523   $240.52   $240.50   $240.50  
  Purchase #3 $34.79   7.588%   $37.4299   $37.43   $37.45   $37.40  
  Purchase #4 $216.63   11.511%   $241.5663   $241.57   $241.55   $241.60  
  Purchase #5 $171.36   13.235%   $194.0395   $194.04   $194.05   $194.00  
  Purchase #6 $202.26   3.728%   $209.8003   $209.80   $209.80   $209.80  
  Purchase #7 $94.98   10.162%   $104.6319   $104.63   $104.65   $104.60  
  7 purchase totals = $1,028.62       $1,124.3958   $1,124.39   $1,124.40   $1,124.30