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 $41.86   11.220%   $46.5567   $46.56   $46.55   $46.60  
  Purchase #2 $97.85   11.413%   $109.0176   $109.02   $109.00   $109.00  
  Purchase #3 $216.26   4.146%   $225.2261   $225.23   $225.25   $225.20  
  Purchase #4 $84.58   10.751%   $93.6732   $93.67   $93.65   $93.70  
  Purchase #5 $240.32   11.233%   $267.3151   $267.32   $267.30   $267.30  
  Purchase #6 $87.77   6.114%   $93.1363   $93.14   $93.15   $93.10  
  Purchase #7 $40.53   6.113%   $43.0076   $43.01   $43.00   $43.00  
  7 purchase totals = $809.17       $877.9326   $877.95   $877.90   $877.90