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 $70.84   7.149%   $75.9044   $75.90   $75.90   $75.90  
  Purchase #2 $112.46   9.777%   $123.4552   $123.46   $123.45   $123.50  
  Purchase #3 $147.56   6.383%   $156.9788   $156.98   $157.00   $157.00  
  Purchase #4 $44.90   3.873%   $46.639   $46.64   $46.65   $46.60  
  Purchase #5 $217.40   11.138%   $241.614   $241.61   $241.60   $241.60  
  Purchase #6 $233.35   7.613%   $251.1149   $251.11   $251.10   $251.10  
  Purchase #7 $104.84   4.283%   $109.3303   $109.33   $109.35   $109.30  
  7 purchase totals = $931.35       $1,005.0366   $1,005.03   $1,005.05   $1,005.00