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 $169.86   9.771%   $186.457   $186.46   $186.45   $186.50  
  Purchase #2 $11.52   13.194%   $13.0399   $13.04   $13.05   $13.00  
  Purchase #3 $246.85   11.275%   $274.6823   $274.68   $274.70   $274.70  
  Purchase #4 $213.69   5.787%   $226.0562   $226.06   $226.05   $226.10  
  Purchase #5 $87.63   4.862%   $91.8906   $91.89   $91.90   $91.90  
  Purchase #6 $50.54   13.504%   $57.3649   $57.36   $57.35   $57.40  
  Purchase #7 $187.48   12.505%   $210.9244   $210.92   $210.90   $210.90  
  7 purchase totals = $967.57       $1,060.4153   $1,060.41   $1,060.40   $1,060.50