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 $238.57   13.144%   $269.9276   $269.93   $269.95   $269.90  
  Purchase #2 $176.97   8.481%   $191.9788   $191.98   $192.00   $192.00  
  Purchase #3 $59.57   10.126%   $65.6021   $65.60   $65.60   $65.60  
  Purchase #4 $35.44   9.625%   $38.8511   $38.85   $38.85   $38.90  
  Purchase #5 $64.56   8.185%   $69.8442   $69.84   $69.85   $69.80  
  Purchase #6 $211.74   7.513%   $227.648   $227.65   $227.65   $227.60  
  Purchase #7 $135.36   11.557%   $151.0036   $151.00   $151.00   $151.00  
  7 purchase totals = $922.21       $1,014.8554   $1,014.85   $1,014.90   $1,014.80