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 $43.31   12.292%   $48.6337   $48.63   $48.65   $48.60  
  Purchase #2 $113.42   9.229%   $123.8875   $123.89   $123.90   $123.90  
  Purchase #3 $8.92   7.351%   $9.5757   $9.58   $9.60   $9.60  
  Purchase #4 $239.51   12.459%   $269.3506   $269.35   $269.35   $269.40  
  Purchase #5 $217.33   12.563%   $244.6332   $244.63   $244.65   $244.60  
  Purchase #6 $141.50   4.328%   $147.6241   $147.62   $147.60   $147.60  
  Purchase #7 $173.41   3.248%   $179.0424   $179.04   $179.05   $179.00  
  7 purchase totals = $937.40       $1,022.7472   $1,022.74   $1,022.80   $1,022.70