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 $72.32   3.802%   $75.0696   $75.07   $75.05   $75.10  
  Purchase #2 $72.51   11.288%   $80.6949   $80.69   $80.70   $80.70  
  Purchase #3 $21.98   4.586%   $22.988   $22.99   $23.00   $23.00  
  Purchase #4 $68.58   4.525%   $71.6832   $71.68   $71.70   $71.70  
  Purchase #5 $36.55   3.572%   $37.8556   $37.86   $37.85   $37.90  
  Purchase #6 $142.68   11.302%   $158.8057   $158.81   $158.80   $158.80  
  Purchase #7 $180.74   4.737%   $189.3017   $189.30   $189.30   $189.30  
  7 purchase totals = $595.36       $636.3987   $636.40   $636.40   $636.50