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 $75.51   8.618%   $82.0175   $82.02   $82.00   $82.00  
  Purchase #2 $248.44   11.254%   $276.3994   $276.40   $276.40   $276.40  
  Purchase #3 $99.50   5.744%   $105.2153   $105.22   $105.20   $105.20  
  Purchase #4 $56.67   9.753%   $62.197   $62.20   $62.20   $62.20  
  Purchase #5 $225.80   5.568%   $238.3725   $238.37   $238.35   $238.40  
  Purchase #6 $202.63   11.562%   $226.0581   $226.06   $226.05   $226.10  
  Purchase #7 $88.50   8.737%   $96.2322   $96.23   $96.25   $96.20  
  7 purchase totals = $997.05       $1,086.4920   $1,086.50   $1,086.45   $1,086.50