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 $163.66   6.682%   $174.5958   $174.60   $174.60   $174.60  
  Purchase #2 $67.81   9.760%   $74.4283   $74.43   $74.45   $74.40  
  Purchase #3 $104.71   11.658%   $116.9171   $116.92   $116.90   $116.90  
  Purchase #4 $236.44   6.865%   $252.6716   $252.67   $252.65   $252.70  
  Purchase #5 $155.98   10.547%   $172.4312   $172.43   $172.45   $172.40  
  Purchase #6 $30.60   11.310%   $34.0609   $34.06   $34.05   $34.10  
  Purchase #7 $177.95   6.632%   $189.7516   $189.75   $189.75   $189.80  
  7 purchase totals = $937.15       $1,014.8565   $1,014.86   $1,014.85   $1,014.90