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 $55.50   3.806%   $57.6123   $57.61   $57.60   $57.60  
  Purchase #2 $44.76   11.463%   $49.8908   $49.89   $49.90   $49.90  
  Purchase #3 $73.76   9.216%   $80.5577   $80.56   $80.55   $80.60  
  Purchase #4 $200.99   12.539%   $226.1921   $226.19   $226.20   $226.20  
  Purchase #5 $238.78   5.340%   $251.5309   $251.53   $251.55   $251.50  
  Purchase #6 $156.57   5.872%   $165.7638   $165.76   $165.75   $165.80  
  Purchase #7 $199.89   3.384%   $206.6543   $206.65   $206.65   $206.70  
  7 purchase totals = $970.25       $1,038.2019   $1,038.19   $1,038.20   $1,038.30