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 $121.62   3.208%   $125.5216   $125.52   $125.50   $125.50  
  Purchase #2 $57.51   3.668%   $59.6195   $59.62   $59.60   $59.60  
  Purchase #3 $16.96   12.229%   $19.034   $19.03   $19.05   $19.00  
  Purchase #4 $185.28   4.233%   $193.1229   $193.12   $193.10   $193.10  
  Purchase #5 $155.30   6.185%   $164.9053   $164.91   $164.90   $164.90  
  Purchase #6 $193.70   6.499%   $206.2886   $206.29   $206.30   $206.30  
  Purchase #7 $96.85   12.181%   $108.6473   $108.65   $108.65   $108.60  
  7 purchase totals = $827.22       $877.1392   $877.14   $877.10   $877.00