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 $183.49   5.872%   $194.2645   $194.26   $194.25   $194.30  
  Purchase #2 $91.70   5.654%   $96.8847   $96.88   $96.90   $96.90  
  Purchase #3 $191.32   5.454%   $201.7546   $201.75   $201.75   $201.80  
  Purchase #4 $22.35   12.343%   $25.1087   $25.11   $25.10   $25.10  
  Purchase #5 $165.67   6.698%   $176.7666   $176.77   $176.75   $176.80  
  Purchase #6 $130.46   10.341%   $143.9509   $143.95   $143.95   $144.00  
  Purchase #7 $179.27   9.705%   $196.6682   $196.67   $196.65   $196.70  
  7 purchase totals = $964.26       $1,035.3982   $1,035.39   $1,035.35   $1,035.60