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 $60.98   7.660%   $65.6511   $65.65   $65.65   $65.70  
  Purchase #2 $27.75   5.758%   $29.3478   $29.35   $29.35   $29.30  
  Purchase #3 $122.76   3.821%   $127.4507   $127.45   $127.45   $127.50  
  Purchase #4 $31.99   9.301%   $34.9654   $34.97   $34.95   $35.00  
  Purchase #5 $160.69   5.288%   $169.1873   $169.19   $169.20   $169.20  
  Purchase #6 $233.95   4.269%   $243.9373   $243.94   $243.95   $243.90  
  Purchase #7 $30.28   6.652%   $32.2942   $32.29   $32.30   $32.30  
  7 purchase totals = $668.40       $702.8338   $702.84   $702.85   $702.90