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 $61.50   12.165%   $68.9815   $68.98   $69.00   $69.00  
  Purchase #2 $187.91   12.733%   $211.8366   $211.84   $211.85   $211.80  
  Purchase #3 $134.25   13.656%   $152.5832   $152.58   $152.60   $152.60  
  Purchase #4 $58.30   11.324%   $64.9019   $64.90   $64.90   $64.90  
  Purchase #5 $201.68   7.449%   $216.7031   $216.70   $216.70   $216.70  
  Purchase #6 $84.35   3.624%   $87.4068   $87.41   $87.40   $87.40  
  Purchase #7 $120.27   6.416%   $127.9865   $127.99   $128.00   $128.00  
  7 purchase totals = $848.26       $930.3996   $930.40   $930.45   $930.40