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 $60.67   4.163%   $63.1957   $63.20   $63.20   $63.20  
  Purchase #2 $109.68   12.864%   $123.7892   $123.79   $123.80   $123.80  
  Purchase #3 $160.54   11.698%   $179.32   $179.32   $179.30   $179.30  
  Purchase #4 $194.49   11.263%   $216.3954   $216.40   $216.40   $216.40  
  Purchase #5 $55.55   11.779%   $62.0932   $62.09   $62.10   $62.10  
  Purchase #6 $227.74   12.401%   $255.982   $255.98   $256.00   $256.00  
  Purchase #7 $181.54   5.751%   $191.9804   $191.98   $192.00   $192.00  
  7 purchase totals = $990.21       $1,092.7559   $1,092.76   $1,092.80   $1,092.80