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 $229.30   6.754%   $244.7869   $244.79   $244.80   $244.80  
  Purchase #2 $24.40   5.107%   $25.6461   $25.65   $25.65   $25.60  
  Purchase #3 $56.57   7.599%   $60.8688   $60.87   $60.85   $60.90  
  Purchase #4 $199.78   11.352%   $222.459   $222.46   $222.45   $222.50  
  Purchase #5 $127.90   4.806%   $134.0469   $134.05   $134.05   $134.00  
  Purchase #6 $71.44   12.803%   $80.5865   $80.59   $80.60   $80.60  
  Purchase #7 $176.79   8.492%   $191.803   $191.80   $191.80   $191.80  
  7 purchase totals = $886.18       $960.1972   $960.21   $960.20   $960.20