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 $188.91   11.705%   $211.0219   $211.02   $211.00   $211.00  
  Purchase #2 $138.46   6.627%   $147.6357   $147.64   $147.65   $147.60  
  Purchase #3 $114.38   9.121%   $124.8126   $124.81   $124.80   $124.80  
  Purchase #4 $222.85   6.720%   $237.8255   $237.83   $237.85   $237.80  
  Purchase #5 $159.65   12.288%   $179.2678   $179.27   $179.25   $179.30  
  Purchase #6 $21.39   10.132%   $23.5572   $23.56   $23.55   $23.60  
  Purchase #7 $198.85   6.613%   $212   $212.00   $212.00   $212.00  
  7 purchase totals = $1,044.49       $1,136.1207   $1,136.13   $1,136.10   $1,136.10