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 $56.71   10.343%   $62.5755   $62.58   $62.60   $62.60  
  Purchase #2 $188.95   7.871%   $203.8223   $203.82   $203.80   $203.80  
  Purchase #3 $214.54   7.220%   $230.0298   $230.03   $230.05   $230.00  
  Purchase #4 $209.65   7.166%   $224.6735   $224.67   $224.65   $224.70  
  Purchase #5 $145.75   6.824%   $155.696   $155.70   $155.70   $155.70  
  Purchase #6 $38.62   3.398%   $39.9323   $39.93   $39.95   $39.90  
  Purchase #7 $53.67   8.418%   $58.1879   $58.19   $58.20   $58.20  
  7 purchase totals = $907.89       $974.9173   $974.92   $974.95   $974.90