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 $52.65   11.371%   $58.6368   $58.64   $58.65   $58.60  
  Purchase #2 $82.38   3.534%   $85.2913   $85.29   $85.30   $85.30  
  Purchase #3 $108.42   3.777%   $112.515   $112.52   $112.50   $112.50  
  Purchase #4 $226.69   8.869%   $246.7951   $246.80   $246.80   $246.80  
  Purchase #5 $130.79   11.298%   $145.5667   $145.57   $145.55   $145.60  
  Purchase #6 $122.92   5.240%   $129.361   $129.36   $129.35   $129.40  
  Purchase #7 $235.76   13.245%   $266.9864   $266.99   $267.00   $267.00  
  7 purchase totals = $959.61       $1,045.1523   $1,045.17   $1,045.15   $1,045.20