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 $77.47   13.696%   $88.0803   $88.08   $88.10   $88.10  
  Purchase #2 $171.29   4.254%   $178.5767   $178.58   $178.60   $178.60  
  Purchase #3 $200.86   4.688%   $210.2763   $210.28   $210.30   $210.30  
  Purchase #4 $247.26   7.394%   $265.5424   $265.54   $265.55   $265.50  
  Purchase #5 $157.53   11.205%   $175.1812   $175.18   $175.20   $175.20  
  Purchase #6 $6.43   7.604%   $6.9189   $6.92   $6.90   $6.90  
  Purchase #7 $101.50   7.151%   $108.7583   $108.76   $108.75   $108.80  
  7 purchase totals = $962.34       $1,033.3341   $1,033.34   $1,033.40   $1,033.40