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 $191.78   12.243%   $215.2596   $215.26   $215.25   $215.30  
  Purchase #2 $158.31   11.543%   $176.5837   $176.58   $176.60   $176.60  
  Purchase #3 $81.30   12.362%   $91.3503   $91.35   $91.35   $91.40  
  Purchase #4 $59.75   12.226%   $67.055   $67.06   $67.05   $67.10  
  Purchase #5 $211.39   6.638%   $225.4221   $225.42   $225.40   $225.40  
  Purchase #6 $181.87   10.757%   $201.4338   $201.43   $201.45   $201.40  
  Purchase #7 $167.99   5.265%   $176.8347   $176.83   $176.85   $176.80  
  7 purchase totals = $1,052.39       $1,153.9392   $1,153.93   $1,153.95   $1,154.00