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 $173.83   6.277%   $184.7413   $184.74   $184.75   $184.70  
  Purchase #2 $72.91   3.134%   $75.195   $75.20   $75.20   $75.20  
  Purchase #3 $196.92   3.608%   $204.0249   $204.02   $204.00   $204.00  
  Purchase #4 $91.87   5.314%   $96.752   $96.75   $96.75   $96.80  
  Purchase #5 $187.93   6.251%   $199.6775   $199.68   $199.70   $199.70  
  Purchase #6 $107.56   13.666%   $122.2591   $122.26   $122.25   $122.30  
  Purchase #7 $38.53   7.341%   $41.3585   $41.36   $41.35   $41.40  
  7 purchase totals = $869.55       $924.0083   $924.01   $924.00   $924.10