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 $89.29   3.839%   $92.7178   $92.72   $92.70   $92.70  
  Purchase #2 $60.70   11.479%   $67.6678   $67.67   $67.65   $67.70  
  Purchase #3 $66.77   7.273%   $71.6262   $71.63   $71.65   $71.60  
  Purchase #4 $197.72   4.407%   $206.4335   $206.43   $206.45   $206.40  
  Purchase #5 $232.88   3.767%   $241.6526   $241.65   $241.65   $241.70  
  Purchase #6 $16.43   5.610%   $17.3517   $17.35   $17.35   $17.40  
  Purchase #7 $68.93   5.538%   $72.7473   $72.75   $72.75   $72.70  
  7 purchase totals = $732.72       $770.1969   $770.20   $770.20   $770.20