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 $135.53   3.599%   $140.4077   $140.41   $140.40   $140.40  
  Purchase #2 $46.61   12.340%   $52.3617   $52.36   $52.35   $52.40  
  Purchase #3 $36.97   3.135%   $38.129   $38.13   $38.15   $38.10  
  Purchase #4 $33.56   9.702%   $36.816   $36.82   $36.80   $36.80  
  Purchase #5 $80.93   10.609%   $89.5159   $89.52   $89.50   $89.50  
  Purchase #6 $27.50   4.716%   $28.7969   $28.80   $28.80   $28.80  
  Purchase #7 $78.78   8.781%   $85.6977   $85.70   $85.70   $85.70  
  7 purchase totals = $439.88       $471.7249   $471.74   $471.70   $471.70