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 $176.28   12.345%   $198.0418   $198.04   $198.05   $198.00  
  Purchase #2 $92.58   4.135%   $96.4082   $96.41   $96.40   $96.40  
  Purchase #3 $41.76   4.723%   $43.7323   $43.73   $43.75   $43.70  
  Purchase #4 $111.89   5.869%   $118.4568   $118.46   $118.45   $118.50  
  Purchase #5 $44.98   4.572%   $47.0365   $47.04   $47.05   $47.00  
  Purchase #6 $112.78   3.456%   $116.6777   $116.68   $116.70   $116.70  
  Purchase #7 $101.34   6.171%   $107.5937   $107.59   $107.60   $107.60  
  7 purchase totals = $681.61       $727.9470   $727.95   $728.00   $727.90