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 $31.34   7.424%   $33.6667   $33.67   $33.65   $33.70  
  Purchase #2 $89.67   9.205%   $97.9241   $97.92   $97.90   $97.90  
  Purchase #3 $246.47   10.639%   $272.6919   $272.69   $272.70   $272.70  
  Purchase #4 $153.84   3.372%   $159.0275   $159.03   $159.05   $159.00  
  Purchase #5 $111.77   6.156%   $118.6506   $118.65   $118.65   $118.70  
  Purchase #6 $219.74   8.672%   $238.7959   $238.80   $238.80   $238.80  
  Purchase #7 $96.26   7.233%   $103.2225   $103.22   $103.20   $103.20  
  7 purchase totals = $949.09       $1,023.9792   $1,023.98   $1,023.95   $1,024.00