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 $229.98   6.838%   $245.706   $245.71   $245.70   $245.70  
  Purchase #2 $205.88   12.615%   $231.8518   $231.85   $231.85   $231.90  
  Purchase #3 $240.56   13.208%   $272.3332   $272.33   $272.35   $272.30  
  Purchase #4 $9.85   9.668%   $10.8023   $10.80   $10.80   $10.80  
  Purchase #5 $9.81   9.317%   $10.724   $10.72   $10.70   $10.70  
  Purchase #6 $20.83   13.846%   $23.7141   $23.71   $23.70   $23.70  
  Purchase #7 $163.28   10.311%   $180.1158   $180.12   $180.10   $180.10  
  7 purchase totals = $880.19       $975.2472   $975.24   $975.20   $975.20