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 $161.89   7.593%   $174.1823   $174.18   $174.20   $174.20  
  Purchase #2 $99.30   5.417%   $104.6791   $104.68   $104.70   $104.70  
  Purchase #3 $74.77   11.166%   $83.1188   $83.12   $83.10   $83.10  
  Purchase #4 $114.76   10.349%   $126.6365   $126.64   $126.65   $126.60  
  Purchase #5 $207.54   13.647%   $235.863   $235.86   $235.85   $235.90  
  Purchase #6 $147.46   12.474%   $165.8542   $165.85   $165.85   $165.90  
  Purchase #7 $186.26   4.816%   $195.2303   $195.23   $195.25   $195.20  
  7 purchase totals = $991.98       $1,085.5642   $1,085.56   $1,085.60   $1,085.60