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 $59.46   3.274%   $61.4067   $61.41   $61.40   $61.40  
  Purchase #2 $207.38   6.524%   $220.9095   $220.91   $220.90   $220.90  
  Purchase #3 $147.72   7.505%   $158.8064   $158.81   $158.80   $158.80  
  Purchase #4 $110.42   8.584%   $119.8985   $119.90   $119.90   $119.90  
  Purchase #5 $36.70   4.565%   $38.3754   $38.38   $38.40   $38.40  
  Purchase #6 $202.95   4.802%   $212.6957   $212.70   $212.70   $212.70  
  Purchase #7 $232.40   3.322%   $240.1203   $240.12   $240.10   $240.10  
  7 purchase totals = $997.03       $1,052.2125   $1,052.23   $1,052.20   $1,052.20