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 $62.48   6.817%   $66.7393   $66.74   $66.75   $66.70  
  Purchase #2 $212.27   9.727%   $232.9175   $232.92   $232.90   $232.90  
  Purchase #3 $31.97   8.573%   $34.7108   $34.71   $34.70   $34.70  
  Purchase #4 $161.28   7.241%   $172.9583   $172.96   $172.95   $173.00  
  Purchase #5 $110.92   5.516%   $117.0383   $117.04   $117.05   $117.00  
  Purchase #6 $72.41   11.540%   $80.7661   $80.77   $80.75   $80.80  
  Purchase #7 $58.49   11.500%   $65.2164   $65.22   $65.20   $65.20  
  7 purchase totals = $709.82       $770.3467   $770.36   $770.30   $770.30