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 $188.48   5.588%   $199.0123   $199.01   $199.00   $199.00  
  Purchase #2 $118.54   13.489%   $134.5299   $134.53   $134.55   $134.50  
  Purchase #3 $58.70   5.471%   $61.9115   $61.91   $61.90   $61.90  
  Purchase #4 $61.82   12.139%   $69.3243   $69.32   $69.30   $69.30  
  Purchase #5 $15.44   9.351%   $16.8838   $16.88   $16.90   $16.90  
  Purchase #6 $25.68   7.182%   $27.5243   $27.52   $27.50   $27.50  
  Purchase #7 $160.56   13.310%   $181.9305   $181.93   $181.95   $181.90  
  7 purchase totals = $629.22       $691.1166   $691.10   $691.10   $691.00