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 $153.76   11.861%   $171.9975   $172.00   $172.00   $172.00  
  Purchase #2 $5.57   12.541%   $6.2685   $6.27   $6.25   $6.30  
  Purchase #3 $195.72   4.329%   $204.1927   $204.19   $204.20   $204.20  
  Purchase #4 $116.88   6.607%   $124.6023   $124.60   $124.60   $124.60  
  Purchase #5 $150.67   11.771%   $168.4054   $168.41   $168.40   $168.40  
  Purchase #6 $112.54   4.107%   $117.162   $117.16   $117.15   $117.20  
  Purchase #7 $236.64   6.294%   $251.5341   $251.53   $251.55   $251.50  
  7 purchase totals = $971.78       $1,044.1625   $1,044.16   $1,044.15   $1,044.20