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 $234.54   5.447%   $247.3154   $247.32   $247.30   $247.30  
  Purchase #2 $237.51   5.582%   $250.7678   $250.77   $250.75   $250.80  
  Purchase #3 $222.59   9.480%   $243.6915   $243.69   $243.70   $243.70  
  Purchase #4 $21.87   12.780%   $24.665   $24.67   $24.65   $24.70  
  Purchase #5 $75.49   6.319%   $80.2602   $80.26   $80.25   $80.30  
  Purchase #6 $126.75   3.581%   $131.2889   $131.29   $131.30   $131.30  
  Purchase #7 $46.49   11.146%   $51.6718   $51.67   $51.65   $51.70  
  7 purchase totals = $965.24       $1,029.6606   $1,029.67   $1,029.60   $1,029.80