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 $212.35   6.721%   $226.622   $226.62   $226.60   $226.60  
  Purchase #2 $243.55   5.270%   $256.3851   $256.39   $256.40   $256.40  
  Purchase #3 $47.29   11.653%   $52.8007   $52.80   $52.80   $52.80  
  Purchase #4 $182.28   6.859%   $194.7826   $194.78   $194.80   $194.80  
  Purchase #5 $183.73   10.779%   $203.5343   $203.53   $203.55   $203.50  
  Purchase #6 $107.74   7.841%   $116.1879   $116.19   $116.20   $116.20  
  Purchase #7 $94.90   3.580%   $98.2974   $98.30   $98.30   $98.30  
  7 purchase totals = $1,071.84       $1,148.6100   $1,148.61   $1,148.65   $1,148.60