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 $245.42   12.805%   $276.846   $276.85   $276.85   $276.80  
  Purchase #2 $11.66   5.512%   $12.3027   $12.30   $12.30   $12.30  
  Purchase #3 $53.96   12.281%   $60.5868   $60.59   $60.60   $60.60  
  Purchase #4 $219.52   4.303%   $228.9659   $228.97   $228.95   $229.00  
  Purchase #5 $231.50   12.106%   $259.5254   $259.53   $259.55   $259.50  
  Purchase #6 $92.78   10.523%   $102.5432   $102.54   $102.55   $102.50  
  Purchase #7 $237.86   12.542%   $267.6924   $267.69   $267.70   $267.70  
  7 purchase totals = $1,092.70       $1,208.4624   $1,208.47   $1,208.50   $1,208.40