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 $36.83   11.574%   $41.0927   $41.09   $41.10   $41.10  
  Purchase #2 $53.41   13.672%   $60.7122   $60.71   $60.70   $60.70  
  Purchase #3 $246.75   6.550%   $262.9121   $262.91   $262.90   $262.90  
  Purchase #4 $153.37   7.215%   $164.4356   $164.44   $164.45   $164.40  
  Purchase #5 $31.98   4.822%   $33.5221   $33.52   $33.50   $33.50  
  Purchase #6 $187.47   8.290%   $203.0113   $203.01   $203.00   $203.00  
  Purchase #7 $41.80   10.297%   $46.1041   $46.10   $46.10   $46.10  
  7 purchase totals = $751.61       $811.7901   $811.78   $811.75   $811.70