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 $242.26   9.333%   $264.8701   $264.87   $264.85   $264.90  
  Purchase #2 $160.40   6.353%   $170.5902   $170.59   $170.60   $170.60  
  Purchase #3 $47.77   4.528%   $49.933   $49.93   $49.95   $49.90  
  Purchase #4 $33.68   11.124%   $37.4266   $37.43   $37.45   $37.40  
  Purchase #5 $190.82   13.219%   $216.0445   $216.04   $216.05   $216.00  
  Purchase #6 $52.93   3.560%   $54.8143   $54.81   $54.80   $54.80  
  Purchase #7 $233.37   7.642%   $251.2041   $251.20   $251.20   $251.20  
  7 purchase totals = $961.23       $1,044.8828   $1,044.87   $1,044.90   $1,044.80