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 $34.38   11.399%   $38.299   $38.30   $38.30   $38.30  
  Purchase #2 $153.42   8.647%   $166.6862   $166.69   $166.70   $166.70  
  Purchase #3 $32.44   6.185%   $34.4464   $34.45   $34.45   $34.40  
  Purchase #4 $155.70   12.482%   $175.1345   $175.13   $175.15   $175.10  
  Purchase #5 $202.94   12.841%   $228.9995   $229.00   $229.00   $229.00  
  Purchase #6 $198.71   4.339%   $207.332   $207.33   $207.35   $207.30  
  Purchase #7 $190.97   10.358%   $210.7507   $210.75   $210.75   $210.80  
  7 purchase totals = $968.56       $1,061.6483   $1,061.65   $1,061.70   $1,061.60