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 $152.47   12.787%   $171.9663   $171.97   $171.95   $172.00  
  Purchase #2 $225.52   3.309%   $232.9825   $232.98   $233.00   $233.00  
  Purchase #3 $151.76   3.437%   $156.976   $156.98   $157.00   $157.00  
  Purchase #4 $143.80   13.315%   $162.947   $162.95   $162.95   $162.90  
  Purchase #5 $34.95   7.544%   $37.5866   $37.59   $37.60   $37.60  
  Purchase #6 $233.92   5.572%   $246.954   $246.95   $246.95   $247.00  
  Purchase #7 $187.53   7.200%   $201.0322   $201.03   $201.05   $201.00  
  7 purchase totals = $1,129.95       $1,210.4446   $1,210.45   $1,210.50   $1,210.50