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 $227.69   6.155%   $241.7043   $241.70   $241.70   $241.70  
  Purchase #2 $120.36   4.769%   $126.1   $126.10   $126.10   $126.10  
  Purchase #3 $19.53   12.700%   $22.0103   $22.01   $22.00   $22.00  
  Purchase #4 $46.33   8.716%   $50.3681   $50.37   $50.35   $50.40  
  Purchase #5 $228.29   12.757%   $257.413   $257.41   $257.40   $257.40  
  Purchase #6 $184.82   11.854%   $206.7286   $206.73   $206.75   $206.70  
  Purchase #7 $134.51   13.695%   $152.9311   $152.93   $152.95   $152.90  
  7 purchase totals = $961.53       $1,057.2554   $1,057.25   $1,057.25   $1,057.20