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 $61.85   8.232%   $66.9415   $66.94   $66.95   $66.90  
  Purchase #2 $149.89   11.261%   $166.7691   $166.77   $166.75   $166.80  
  Purchase #3 $178.65   13.243%   $202.3086   $202.31   $202.30   $202.30  
  Purchase #4 $222.88   7.519%   $239.6383   $239.64   $239.65   $239.60  
  Purchase #5 $245.28   13.570%   $278.5645   $278.56   $278.55   $278.60  
  Purchase #6 $173.73   7.704%   $187.1142   $187.11   $187.10   $187.10  
  Purchase #7 $10.47   11.461%   $11.67   $11.67   $11.65   $11.70  
  7 purchase totals = $1,042.75       $1,153.0062   $1,153.00   $1,152.95   $1,153.00