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 $37.60   10.603%   $41.5867   $41.59   $41.60   $41.60  
  Purchase #2 $65.65   3.594%   $68.0095   $68.01   $68.00   $68.00  
  Purchase #3 $244.66   12.790%   $275.952   $275.95   $275.95   $276.00  
  Purchase #4 $153.57   3.731%   $159.2997   $159.30   $159.30   $159.30  
  Purchase #5 $33.87   10.113%   $37.2953   $37.30   $37.30   $37.30  
  Purchase #6 $246.98   10.339%   $272.5153   $272.52   $272.50   $272.50  
  Purchase #7 $163.99   4.836%   $171.9206   $171.92   $171.90   $171.90  
  7 purchase totals = $946.32       $1,026.5791   $1,026.59   $1,026.55   $1,026.60