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 $85.62   8.314%   $92.7384   $92.74   $92.75   $92.70  
  Purchase #2 $177.78   10.818%   $197.0122   $197.01   $197.00   $197.00  
  Purchase #3 $29.70   7.442%   $31.9103   $31.91   $31.90   $31.90  
  Purchase #4 $218.60   10.411%   $241.3584   $241.36   $241.35   $241.40  
  Purchase #5 $228.92   10.121%   $252.089   $252.09   $252.10   $252.10  
  Purchase #6 $123.37   12.623%   $138.943   $138.94   $138.95   $138.90  
  Purchase #7 $221.77   10.455%   $244.9561   $244.96   $244.95   $245.00  
  7 purchase totals = $1,085.76       $1,199.0074   $1,199.01   $1,199.00   $1,199.00