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 $233.75   11.669%   $261.0263   $261.03   $261.05   $261.00  
  Purchase #2 $24.27   4.678%   $25.4054   $25.41   $25.40   $25.40  
  Purchase #3 $129.65   13.841%   $147.5949   $147.59   $147.60   $147.60  
  Purchase #4 $184.52   6.145%   $195.8588   $195.86   $195.85   $195.90  
  Purchase #5 $84.95   12.219%   $95.33   $95.33   $95.35   $95.30  
  Purchase #6 $193.38   11.590%   $215.7927   $215.79   $215.80   $215.80  
  Purchase #7 $67.84   4.734%   $71.0515   $71.05   $71.05   $71.10  
  7 purchase totals = $918.36       $1,012.0596   $1,012.06   $1,012.10   $1,012.10