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 $142.65   10.303%   $157.3472   $157.35   $157.35   $157.30  
  Purchase #2 $222.30   8.109%   $240.3263   $240.33   $240.35   $240.30  
  Purchase #3 $180.36   9.387%   $197.2904   $197.29   $197.30   $197.30  
  Purchase #4 $219.49   9.838%   $241.0834   $241.08   $241.10   $241.10  
  Purchase #5 $88.84   4.570%   $92.9   $92.90   $92.90   $92.90  
  Purchase #6 $29.33   5.857%   $31.0479   $31.05   $31.05   $31.00  
  Purchase #7 $168.67   13.817%   $191.9751   $191.98   $192.00   $192.00  
  7 purchase totals = $1,051.64       $1,151.9703   $1,151.98   $1,152.05   $1,151.90