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 $204.93   10.273%   $225.9825   $225.98   $226.00   $226.00  
  Purchase #2 $163.30   4.722%   $171.011   $171.01   $171.00   $171.00  
  Purchase #3 $49.66   13.429%   $56.3288   $56.33   $56.35   $56.30  
  Purchase #4 $242.52   3.301%   $250.5256   $250.53   $250.55   $250.50  
  Purchase #5 $69.31   9.174%   $75.6685   $75.67   $75.65   $75.70  
  Purchase #6 $186.45   6.405%   $198.3921   $198.39   $198.40   $198.40  
  Purchase #7 $152.80   3.431%   $158.0426   $158.04   $158.05   $158.00  
  7 purchase totals = $1,068.97       $1,135.9511   $1,135.95   $1,136.00   $1,135.90