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 $34.64   8.280%   $37.5082   $37.51   $37.50   $37.50  
  Purchase #2 $146.97   7.442%   $157.9075   $157.91   $157.90   $157.90  
  Purchase #3 $162.96   6.553%   $173.6388   $173.64   $173.65   $173.60  
  Purchase #4 $71.74   7.350%   $77.0129   $77.01   $77.00   $77.00  
  Purchase #5 $181.49   13.836%   $206.601   $206.60   $206.60   $206.60  
  Purchase #6 $23.58   13.655%   $26.7998   $26.80   $26.80   $26.80  
  Purchase #7 $191.45   7.516%   $205.8394   $205.84   $205.85   $205.80  
  7 purchase totals = $812.83       $885.3076   $885.31   $885.30   $885.20