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 $184.46   10.330%   $203.5147   $203.51   $203.50   $203.50  
  Purchase #2 $84.61   4.319%   $88.2643   $88.26   $88.25   $88.30  
  Purchase #3 $147.96   3.156%   $152.6296   $152.63   $152.65   $152.60  
  Purchase #4 $186.66   10.138%   $205.5836   $205.58   $205.60   $205.60  
  Purchase #5 $68.99   6.231%   $73.2888   $73.29   $73.30   $73.30  
  Purchase #6 $115.54   3.833%   $119.9686   $119.97   $119.95   $120.00  
  Purchase #7 $188.66   6.690%   $201.2814   $201.28   $201.30   $201.30  
  7 purchase totals = $976.88       $1,044.5310   $1,044.52   $1,044.55   $1,044.60