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 $79.57   5.492%   $83.94   $83.94   $83.95   $83.90  
  Purchase #2 $65.41   13.406%   $74.1789   $74.18   $74.20   $74.20  
  Purchase #3 $95.86   12.623%   $107.9604   $107.96   $107.95   $108.00  
  Purchase #4 $222.36   5.256%   $234.0472   $234.05   $234.05   $234.00  
  Purchase #5 $220.35   8.830%   $239.8069   $239.81   $239.80   $239.80  
  Purchase #6 $87.35   12.327%   $98.1176   $98.12   $98.10   $98.10  
  Purchase #7 $223.72   3.782%   $232.1811   $232.18   $232.20   $232.20  
  7 purchase totals = $994.62       $1,070.2321   $1,070.24   $1,070.25   $1,070.20