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 $61.69   11.743%   $68.9343   $68.93   $68.95   $68.90  
  Purchase #2 $228.97   13.114%   $258.9971   $259.00   $259.00   $259.00  
  Purchase #3 $200.72   12.373%   $225.5551   $225.56   $225.55   $225.60  
  Purchase #4 $62.52   7.387%   $67.1384   $67.14   $67.15   $67.10  
  Purchase #5 $118.74   11.443%   $132.3274   $132.33   $132.35   $132.30  
  Purchase #6 $220.25   8.449%   $238.8589   $238.86   $238.85   $238.90  
  Purchase #7 $177.66   8.133%   $192.1091   $192.11   $192.10   $192.10  
  7 purchase totals = $1,070.55       $1,183.9203   $1,183.93   $1,183.95   $1,183.90