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 $83.78   13.199%   $94.8381   $94.84   $94.85   $94.80  
  Purchase #2 $80.69   11.527%   $89.9911   $89.99   $90.00   $90.00  
  Purchase #3 $50.64   10.493%   $55.9537   $55.95   $55.95   $56.00  
  Purchase #4 $245.62   6.754%   $262.2092   $262.21   $262.20   $262.20  
  Purchase #5 $58.98   6.365%   $62.7341   $62.73   $62.75   $62.70  
  Purchase #6 $241.32   4.162%   $251.3637   $251.36   $251.35   $251.40  
  Purchase #7 $53.55   6.745%   $57.1619   $57.16   $57.15   $57.20  
  7 purchase totals = $814.58       $874.2518   $874.24   $874.25   $874.30