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 $131.82   3.735%   $136.7435   $136.74   $136.75   $136.70  
  Purchase #2 $246.91   12.123%   $276.8429   $276.84   $276.85   $276.80  
  Purchase #3 $9.30   13.371%   $10.5435   $10.54   $10.55   $10.50  
  Purchase #4 $135.47   8.699%   $147.2545   $147.25   $147.25   $147.30  
  Purchase #5 $65.83   3.464%   $68.1104   $68.11   $68.10   $68.10  
  Purchase #6 $232.55   12.132%   $260.763   $260.76   $260.75   $260.80  
  Purchase #7 $205.70   11.850%   $230.0755   $230.08   $230.10   $230.10  
  7 purchase totals = $1,027.58       $1,130.3333   $1,130.32   $1,130.35   $1,130.30