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 $111.66   8.379%   $121.016   $121.02   $121.00   $121.00  
  Purchase #2 $78.81   13.348%   $89.3296   $89.33   $89.35   $89.30  
  Purchase #3 $56.58   10.736%   $62.6544   $62.65   $62.65   $62.70  
  Purchase #4 $203.82   3.751%   $211.4653   $211.47   $211.45   $211.50  
  Purchase #5 $169.78   11.697%   $189.6392   $189.64   $189.65   $189.60  
  Purchase #6 $224.43   12.385%   $252.2257   $252.23   $252.25   $252.20  
  Purchase #7 $217.97   11.549%   $243.1434   $243.14   $243.15   $243.10  
  7 purchase totals = $1,063.05       $1,169.4736   $1,169.48   $1,169.50   $1,169.40