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 $208.29   8.220%   $225.4114   $225.41   $225.40   $225.40  
  Purchase #2 $145.82   5.246%   $153.4697   $153.47   $153.45   $153.50  
  Purchase #3 $60.28   5.446%   $63.5628   $63.56   $63.55   $63.60  
  Purchase #4 $249.64   7.463%   $268.2706   $268.27   $268.25   $268.30  
  Purchase #5 $210.98   4.502%   $220.4783   $220.48   $220.50   $220.50  
  Purchase #6 $141.47   8.742%   $153.8373   $153.84   $153.85   $153.80  
  Purchase #7 $241.60   5.778%   $255.5596   $255.56   $255.55   $255.60  
  7 purchase totals = $1,258.08       $1,340.5897   $1,340.59   $1,340.55   $1,340.70