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 $53.80   13.390%   $61.0038   $61.00   $61.00   $61.00  
  Purchase #2 $174.55   11.805%   $195.1556   $195.16   $195.15   $195.20  
  Purchase #3 $216.88   12.352%   $243.669   $243.67   $243.65   $243.70  
  Purchase #4 $129.61   12.278%   $145.5235   $145.52   $145.50   $145.50  
  Purchase #5 $41.81   11.537%   $46.6336   $46.63   $46.65   $46.60  
  Purchase #6 $82.72   12.406%   $92.9822   $92.98   $93.00   $93.00  
  Purchase #7 $246.29   12.708%   $277.5885   $277.59   $277.60   $277.60  
  7 purchase totals = $945.66       $1,062.5562   $1,062.55   $1,062.55   $1,062.60