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 $237.54   12.382%   $266.9522   $266.95   $266.95   $267.00  
  Purchase #2 $32.70   12.679%   $36.846   $36.85   $36.85   $36.80  
  Purchase #3 $249.33   5.858%   $263.9358   $263.94   $263.95   $263.90  
  Purchase #4 $111.99   9.413%   $122.5316   $122.53   $122.55   $122.50  
  Purchase #5 $153.84   5.645%   $162.5243   $162.52   $162.50   $162.50  
  Purchase #6 $192.99   9.196%   $210.7374   $210.74   $210.75   $210.70  
  Purchase #7 $199.36   6.675%   $212.6673   $212.67   $212.65   $212.70  
  7 purchase totals = $1,177.75       $1,276.1946   $1,276.20   $1,276.20   $1,276.10