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 $118.72   9.869%   $130.4365   $130.44   $130.45   $130.40  
  Purchase #2 $238.44   11.829%   $266.6451   $266.65   $266.65   $266.60  
  Purchase #3 $125.81   7.780%   $135.598   $135.60   $135.60   $135.60  
  Purchase #4 $21.93   8.494%   $23.7927   $23.79   $23.80   $23.80  
  Purchase #5 $69.50   5.415%   $73.2634   $73.26   $73.25   $73.30  
  Purchase #6 $131.66   7.769%   $141.8887   $141.89   $141.90   $141.90  
  Purchase #7 $165.77   6.384%   $176.3528   $176.35   $176.35   $176.40  
  7 purchase totals = $871.83       $947.9772   $947.98   $948.00   $948.00