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 $69.59   6.312%   $73.9825   $73.98   $74.00   $74.00  
  Purchase #2 $80.37   13.752%   $91.4225   $91.42   $91.40   $91.40  
  Purchase #3 $112.77   6.684%   $120.3075   $120.31   $120.30   $120.30  
  Purchase #4 $94.41   5.661%   $99.7546   $99.75   $99.75   $99.80  
  Purchase #5 $191.52   4.535%   $200.2054   $200.21   $200.20   $200.20  
  Purchase #6 $94.69   12.153%   $106.1977   $106.20   $106.20   $106.20  
  Purchase #7 $12.37   8.428%   $13.4125   $13.41   $13.40   $13.40  
  7 purchase totals = $655.72       $705.2827   $705.28   $705.25   $705.30