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 $121.68   11.851%   $136.1003   $136.10   $136.10   $136.10  
  Purchase #2 $49.47   13.113%   $55.957   $55.96   $55.95   $56.00  
  Purchase #3 $33.90   12.346%   $38.0853   $38.09   $38.10   $38.10  
  Purchase #4 $193.78   9.447%   $212.0864   $212.09   $212.10   $212.10  
  Purchase #5 $58.34   4.422%   $60.9198   $60.92   $60.90   $60.90  
  Purchase #6 $247.30   6.264%   $262.7909   $262.79   $262.80   $262.80  
  Purchase #7 $170.67   6.612%   $181.9547   $181.95   $181.95   $182.00  
  7 purchase totals = $875.14       $947.8944   $947.90   $947.90   $948.00