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 $243.86   6.309%   $259.2451   $259.25   $259.25   $259.20  
  Purchase #2 $134.35   11.556%   $149.8755   $149.88   $149.90   $149.90  
  Purchase #3 $98.60   9.187%   $107.6584   $107.66   $107.65   $107.70  
  Purchase #4 $203.55   11.119%   $226.1827   $226.18   $226.20   $226.20  
  Purchase #5 $55.55   9.559%   $60.86   $60.86   $60.85   $60.90  
  Purchase #6 $197.74   7.665%   $212.8968   $212.90   $212.90   $212.90  
  Purchase #7 $35.82   4.528%   $37.4419   $37.44   $37.45   $37.40  
  7 purchase totals = $969.47       $1,054.1604   $1,054.17   $1,054.20   $1,054.20