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 $167.95   6.461%   $178.8012   $178.80   $178.80   $178.80  
  Purchase #2 $216.38   8.353%   $234.4542   $234.45   $234.45   $234.50  
  Purchase #3 $112.57   10.735%   $124.6544   $124.65   $124.65   $124.70  
  Purchase #4 $167.93   12.848%   $189.5056   $189.51   $189.50   $189.50  
  Purchase #5 $249.97   5.636%   $264.0583   $264.06   $264.05   $264.10  
  Purchase #6 $23.27   9.189%   $25.4083   $25.41   $25.40   $25.40  
  Purchase #7 $33.84   10.351%   $37.3428   $37.34   $37.35   $37.30  
  7 purchase totals = $971.91       $1,054.2248   $1,054.22   $1,054.20   $1,054.30