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 $94.74   7.403%   $101.7536   $101.75   $101.75   $101.80  
  Purchase #2 $184.69   6.296%   $196.3181   $196.32   $196.30   $196.30  
  Purchase #3 $56.76   8.632%   $61.6595   $61.66   $61.65   $61.70  
  Purchase #4 $202.45   12.232%   $227.2137   $227.21   $227.20   $227.20  
  Purchase #5 $247.83   13.382%   $280.9946   $280.99   $281.00   $281.00  
  Purchase #6 $138.25   12.207%   $155.1262   $155.13   $155.15   $155.10  
  Purchase #7 $30.33   11.207%   $33.7291   $33.73   $33.75   $33.70  
  7 purchase totals = $955.05       $1,056.7948   $1,056.79   $1,056.80   $1,056.80