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 $32.58   3.290%   $33.6519   $33.65   $33.65   $33.70  
  Purchase #2 $95.95   11.508%   $106.9919   $106.99   $107.00   $107.00  
  Purchase #3 $20.67   3.542%   $21.4021   $21.40   $21.40   $21.40  
  Purchase #4 $225.57   4.404%   $235.5041   $235.50   $235.50   $235.50  
  Purchase #5 $162.97   9.470%   $178.4033   $178.40   $178.40   $178.40  
  Purchase #6 $68.42   7.203%   $73.3483   $73.35   $73.35   $73.30  
  Purchase #7 $51.25   4.310%   $53.4589   $53.46   $53.45   $53.50  
  7 purchase totals = $657.41       $702.7605   $702.75   $702.75   $702.80