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 $215.56   12.116%   $241.6772   $241.68   $241.70   $241.70  
  Purchase #2 $186.52   7.873%   $201.2047   $201.20   $201.20   $201.20  
  Purchase #3 $246.37   5.337%   $259.5188   $259.52   $259.50   $259.50  
  Purchase #4 $193.41   13.293%   $219.12   $219.12   $219.10   $219.10  
  Purchase #5 $116.50   4.354%   $121.5724   $121.57   $121.55   $121.60  
  Purchase #6 $137.66   4.753%   $144.203   $144.20   $144.20   $144.20  
  Purchase #7 $12.33   13.283%   $13.9678   $13.97   $13.95   $14.00  
  7 purchase totals = $1,108.35       $1,201.2639   $1,201.26   $1,201.20   $1,201.30