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 $178.62   13.650%   $203.0016   $203.00   $203.00   $203.00  
  Purchase #2 $211.67   3.728%   $219.5611   $219.56   $219.55   $219.60  
  Purchase #3 $21.43   11.149%   $23.8192   $23.82   $23.80   $23.80  
  Purchase #4 $117.54   8.428%   $127.4463   $127.45   $127.45   $127.40  
  Purchase #5 $102.32   3.244%   $105.6393   $105.64   $105.65   $105.60  
  Purchase #6 $164.68   11.539%   $183.6824   $183.68   $183.70   $183.70  
  Purchase #7 $141.99   5.481%   $149.7725   $149.77   $149.75   $149.80  
  7 purchase totals = $938.25       $1,012.9224   $1,012.92   $1,012.90   $1,012.90