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 $138.71   3.500%   $143.5649   $143.56   $143.55   $143.60  
  Purchase #2 $111.40   6.765%   $118.9362   $118.94   $118.95   $118.90  
  Purchase #3 $195.54   4.498%   $204.3354   $204.34   $204.35   $204.30  
  Purchase #4 $157.59   13.406%   $178.7165   $178.72   $178.70   $178.70  
  Purchase #5 $218.85   5.164%   $230.1514   $230.15   $230.15   $230.20  
  Purchase #6 $31.97   7.148%   $34.2552   $34.26   $34.25   $34.30  
  Purchase #7 $200.41   12.324%   $225.1085   $225.11   $225.10   $225.10  
  7 purchase totals = $1,054.47       $1,135.0681   $1,135.08   $1,135.05   $1,135.10