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 $194.52   4.461%   $203.1975   $203.20   $203.20   $203.20  
  Purchase #2 $124.57   12.264%   $139.8473   $139.85   $139.85   $139.80  
  Purchase #3 $191.39   6.225%   $203.304   $203.30   $203.30   $203.30  
  Purchase #4 $191.42   10.349%   $211.2301   $211.23   $211.25   $211.20  
  Purchase #5 $58.64   12.174%   $65.7788   $65.78   $65.80   $65.80  
  Purchase #6 $136.50   5.534%   $144.0539   $144.05   $144.05   $144.10  
  Purchase #7 $152.85   10.667%   $169.1545   $169.15   $169.15   $169.20  
  7 purchase totals = $1,049.89       $1,136.5661   $1,136.56   $1,136.60   $1,136.60