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 $91.25   5.818%   $96.5589   $96.56   $96.55   $96.60  
  Purchase #2 $188.96   12.647%   $212.8578   $212.86   $212.85   $212.90  
  Purchase #3 $244.64   3.739%   $253.7871   $253.79   $253.80   $253.80  
  Purchase #4 $246.32   7.645%   $265.1512   $265.15   $265.15   $265.20  
  Purchase #5 $17.42   11.253%   $19.3803   $19.38   $19.40   $19.40  
  Purchase #6 $112.90   8.540%   $122.5417   $122.54   $122.55   $122.50  
  Purchase #7 $213.77   6.174%   $226.9682   $226.97   $226.95   $227.00  
  7 purchase totals = $1,115.26       $1,197.2452   $1,197.25   $1,197.25   $1,197.40