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 $157.25   4.650%   $164.5621   $164.56   $164.55   $164.60  
  Purchase #2 $224.60   11.751%   $250.9927   $250.99   $251.00   $251.00  
  Purchase #3 $60.34   9.226%   $65.907   $65.91   $65.90   $65.90  
  Purchase #4 $78.27   12.372%   $87.9536   $87.95   $87.95   $88.00  
  Purchase #5 $65.55   12.205%   $73.5504   $73.55   $73.55   $73.60  
  Purchase #6 $160.92   9.548%   $176.2846   $176.28   $176.30   $176.30  
  Purchase #7 $179.68   12.223%   $201.6423   $201.64   $201.65   $201.60  
  7 purchase totals = $926.61       $1,020.8927   $1,020.88   $1,020.90   $1,021.00