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 $86.82   8.109%   $93.8602   $93.86   $93.85   $93.90  
  Purchase #2 $153.59   5.244%   $161.6443   $161.64   $161.65   $161.60  
  Purchase #3 $189.72   6.759%   $202.5432   $202.54   $202.55   $202.50  
  Purchase #4 $174.77   5.479%   $184.3456   $184.35   $184.35   $184.30  
  Purchase #5 $76.98   8.678%   $83.6603   $83.66   $83.65   $83.70  
  Purchase #6 $144.56   11.398%   $161.0369   $161.04   $161.05   $161.00  
  Purchase #7 $231.26   9.848%   $254.0345   $254.03   $254.05   $254.00  
  7 purchase totals = $1,057.70       $1,141.1250   $1,141.12   $1,141.15   $1,141.00