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 $59.30   10.446%   $65.4945   $65.49   $65.50   $65.50  
  Purchase #2 $168.66   13.283%   $191.0631   $191.06   $191.05   $191.10  
  Purchase #3 $153.85   12.380%   $172.8966   $172.90   $172.90   $172.90  
  Purchase #4 $231.44   6.868%   $247.3353   $247.34   $247.35   $247.30  
  Purchase #5 $246.96   6.609%   $263.2816   $263.28   $263.30   $263.30  
  Purchase #6 $26.39   9.180%   $28.8126   $28.81   $28.80   $28.80  
  Purchase #7 $140.51   9.489%   $153.843   $153.84   $153.85   $153.80  
  7 purchase totals = $1,027.11       $1,122.7267   $1,122.72   $1,122.75   $1,122.70