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 $201.81   6.788%   $215.5089   $215.51   $215.50   $215.50  
  Purchase #2 $219.29   7.290%   $235.2762   $235.28   $235.30   $235.30  
  Purchase #3 $57.93   10.120%   $63.7925   $63.79   $63.80   $63.80  
  Purchase #4 $35.93   8.310%   $38.9158   $38.92   $38.90   $38.90  
  Purchase #5 $19.95   5.247%   $20.9968   $21.00   $21.00   $21.00  
  Purchase #6 $193.47   11.474%   $215.6687   $215.67   $215.65   $215.70  
  Purchase #7 $226.56   4.319%   $236.3451   $236.35   $236.35   $236.30  
  7 purchase totals = $954.94       $1,026.5040   $1,026.52   $1,026.50   $1,026.50