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 $86.32   12.751%   $97.3267   $97.33   $97.35   $97.30  
  Purchase #2 $12.44   7.328%   $13.3516   $13.35   $13.35   $13.40  
  Purchase #3 $160.86   8.551%   $174.6151   $174.62   $174.60   $174.60  
  Purchase #4 $203.45   12.514%   $228.9097   $228.91   $228.90   $228.90  
  Purchase #5 $147.28   7.534%   $158.3761   $158.38   $158.40   $158.40  
  Purchase #6 $80.76   12.321%   $90.7104   $90.71   $90.70   $90.70  
  Purchase #7 $106.89   9.797%   $117.362   $117.36   $117.35   $117.40  
  7 purchase totals = $798.00       $880.6516   $880.66   $880.65   $880.70