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 $226.75   5.210%   $238.5637   $238.56   $238.55   $238.60  
  Purchase #2 $148.79   4.830%   $155.9766   $155.98   $156.00   $156.00  
  Purchase #3 $202.68   5.477%   $213.7808   $213.78   $213.80   $213.80  
  Purchase #4 $90.61   6.508%   $96.5069   $96.51   $96.50   $96.50  
  Purchase #5 $239.54   3.259%   $247.3466   $247.35   $247.35   $247.30  
  Purchase #6 $51.85   5.699%   $54.8049   $54.80   $54.80   $54.80  
  Purchase #7 $89.93   3.575%   $93.145   $93.15   $93.15   $93.10  
  7 purchase totals = $1,050.15       $1,100.1245   $1,100.13   $1,100.15   $1,100.10