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 $143.44   7.828%   $154.6685   $154.67   $154.65   $154.70  
  Purchase #2 $248.87   5.507%   $262.5753   $262.58   $262.60   $262.60  
  Purchase #3 $131.33   12.328%   $147.5204   $147.52   $147.50   $147.50  
  Purchase #4 $95.48   9.203%   $104.267   $104.27   $104.25   $104.30  
  Purchase #5 $198.64   13.255%   $224.9697   $224.97   $224.95   $225.00  
  Purchase #6 $13.75   5.479%   $14.5034   $14.50   $14.50   $14.50  
  Purchase #7 $22.88   7.487%   $24.593   $24.59   $24.60   $24.60  
  7 purchase totals = $854.39       $933.0973   $933.10   $933.05   $933.20