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 $34.48   6.221%   $36.625   $36.63   $36.65   $36.60  
  Purchase #2 $237.43   12.599%   $267.3438   $267.34   $267.35   $267.30  
  Purchase #3 $182.82   7.477%   $196.4895   $196.49   $196.50   $196.50  
  Purchase #4 $155.78   4.833%   $163.3088   $163.31   $163.30   $163.30  
  Purchase #5 $207.84   9.121%   $226.7971   $226.80   $226.80   $226.80  
  Purchase #6 $157.76   5.723%   $166.7886   $166.79   $166.80   $166.80  
  Purchase #7 $172.98   11.753%   $193.3103   $193.31   $193.30   $193.30  
  7 purchase totals = $1,149.09       $1,250.6631   $1,250.67   $1,250.70   $1,250.60