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 $164.89   6.242%   $175.1824   $175.18   $175.20   $175.20  
  Purchase #2 $225.81   8.677%   $245.4035   $245.40   $245.40   $245.40  
  Purchase #3 $250.61   11.538%   $279.5254   $279.53   $279.55   $279.50  
  Purchase #4 $244.52   13.512%   $277.5595   $277.56   $277.55   $277.60  
  Purchase #5 $43.35   12.751%   $48.8776   $48.88   $48.90   $48.90  
  Purchase #6 $160.63   8.310%   $173.9784   $173.98   $174.00   $174.00  
  Purchase #7 $63.65   4.402%   $66.4519   $66.45   $66.45   $66.50  
  7 purchase totals = $1,153.46       $1,266.9787   $1,266.98   $1,267.05   $1,267.10