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 $195.31   3.570%   $202.2826   $202.28   $202.30   $202.30  
  Purchase #2 $230.53   13.190%   $260.9369   $260.94   $260.95   $260.90  
  Purchase #3 $69.74   5.270%   $73.4153   $73.42   $73.40   $73.40  
  Purchase #4 $29.52   13.515%   $33.5096   $33.51   $33.50   $33.50  
  Purchase #5 $43.28   10.789%   $47.9495   $47.95   $47.95   $47.90  
  Purchase #6 $169.69   13.772%   $193.0597   $193.06   $193.05   $193.10  
  Purchase #7 $235.88   8.552%   $256.0525   $256.05   $256.05   $256.10  
  7 purchase totals = $973.95       $1,067.2061   $1,067.21   $1,067.20   $1,067.20