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 $49.83   8.236%   $53.934   $53.93   $53.95   $53.90  
  Purchase #2 $110.85   13.656%   $125.9877   $125.99   $126.00   $126.00  
  Purchase #3 $119.46   5.404%   $125.9156   $125.92   $125.90   $125.90  
  Purchase #4 $79.65   13.615%   $90.4943   $90.49   $90.50   $90.50  
  Purchase #5 $167.82   9.508%   $183.7763   $183.78   $183.80   $183.80  
  Purchase #6 $165.82   3.248%   $171.2058   $171.21   $171.20   $171.20  
  Purchase #7 $228.35   11.322%   $254.2038   $254.20   $254.20   $254.20  
  7 purchase totals = $921.78       $1,005.5175   $1,005.52   $1,005.55   $1,005.50