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 $188.97   8.215%   $204.4939   $204.49   $204.50   $204.50  
  Purchase #2 $193.75   7.196%   $207.6923   $207.69   $207.70   $207.70  
  Purchase #3 $54.71   3.708%   $56.7386   $56.74   $56.75   $56.70  
  Purchase #4 $88.58   7.131%   $94.8966   $94.90   $94.90   $94.90  
  Purchase #5 $194.68   6.331%   $207.0052   $207.01   $207.00   $207.00  
  Purchase #6 $148.90   9.445%   $162.9636   $162.96   $162.95   $163.00  
  Purchase #7 $191.69   5.109%   $201.4834   $201.48   $201.50   $201.50  
  7 purchase totals = $1,061.28       $1,135.2736   $1,135.27   $1,135.30   $1,135.30