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 $72.41   5.804%   $76.6127   $76.61   $76.60   $76.60  
  Purchase #2 $59.46   10.592%   $65.758   $65.76   $65.75   $65.80  
  Purchase #3 $243.26   3.702%   $252.2655   $252.27   $252.25   $252.30  
  Purchase #4 $205.95   12.852%   $232.4187   $232.42   $232.40   $232.40  
  Purchase #5 $165.73   3.766%   $171.9714   $171.97   $171.95   $172.00  
  Purchase #6 $168.84   6.851%   $180.4072   $180.41   $180.40   $180.40  
  Purchase #7 $186.42   4.245%   $194.3335   $194.33   $194.35   $194.30  
  7 purchase totals = $1,102.07       $1,173.7670   $1,173.77   $1,173.70   $1,173.80