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 $232.79   10.247%   $256.644   $256.64   $256.65   $256.60  
  Purchase #2 $148.33   7.841%   $159.9606   $159.96   $159.95   $160.00  
  Purchase #3 $58.41   13.305%   $66.1815   $66.18   $66.20   $66.20  
  Purchase #4 $231.56   9.372%   $253.2618   $253.26   $253.25   $253.30  
  Purchase #5 $66.91   4.154%   $69.6894   $69.69   $69.70   $69.70  
  Purchase #6 $181.46   4.273%   $189.2138   $189.21   $189.20   $189.20  
  Purchase #7 $50.76   6.191%   $53.9026   $53.90   $53.90   $53.90  
  7 purchase totals = $970.22       $1,048.8537   $1,048.84   $1,048.85   $1,048.90