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 $169.25   10.437%   $186.9146   $186.91   $186.90   $186.90  
  Purchase #2 $62.73   12.618%   $70.6453   $70.65   $70.65   $70.60  
  Purchase #3 $58.54   6.855%   $62.5529   $62.55   $62.55   $62.60  
  Purchase #4 $121.91   10.401%   $134.5899   $134.59   $134.60   $134.60  
  Purchase #5 $127.64   6.482%   $135.9136   $135.91   $135.90   $135.90  
  Purchase #6 $222.82   6.721%   $237.7957   $237.80   $237.80   $237.80  
  Purchase #7 $175.59   5.117%   $184.5749   $184.57   $184.55   $184.60  
  7 purchase totals = $938.48       $1,012.9869   $1,012.98   $1,012.95   $1,013.00