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 $61.65   9.247%   $67.3508   $67.35   $67.35   $67.40  
  Purchase #2 $219.59   12.154%   $246.279   $246.28   $246.30   $246.30  
  Purchase #3 $19.52   11.708%   $21.8054   $21.81   $21.80   $21.80  
  Purchase #4 $121.38   10.435%   $134.046   $134.05   $134.05   $134.00  
  Purchase #5 $147.83   9.162%   $161.3742   $161.37   $161.35   $161.40  
  Purchase #6 $218.51   11.197%   $242.9766   $242.98   $243.00   $243.00  
  Purchase #7 $125.65   12.127%   $140.8876   $140.89   $140.90   $140.90  
  7 purchase totals = $914.13       $1,014.7196   $1,014.73   $1,014.75   $1,014.80