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 $84.34   8.551%   $91.5519   $91.55   $91.55   $91.60  
  Purchase #2 $130.89   11.467%   $145.8992   $145.90   $145.90   $145.90  
  Purchase #3 $246.95   11.739%   $275.9395   $275.94   $275.95   $275.90  
  Purchase #4 $123.26   9.437%   $134.892   $134.89   $134.90   $134.90  
  Purchase #5 $162.26   13.411%   $184.0207   $184.02   $184.00   $184.00  
  Purchase #6 $55.34   11.223%   $61.5508   $61.55   $61.55   $61.60  
  Purchase #7 $152.96   5.225%   $160.9522   $160.95   $160.95   $161.00  
  7 purchase totals = $956.00       $1,054.8063   $1,054.80   $1,054.80   $1,054.90