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 $150.94   10.640%   $167   $167.00   $167.00   $167.00  
  Purchase #2 $248.31   13.214%   $281.1217   $281.12   $281.10   $281.10  
  Purchase #3 $73.48   5.328%   $77.395   $77.40   $77.40   $77.40  
  Purchase #4 $28.33   3.568%   $29.3408   $29.34   $29.35   $29.30  
  Purchase #5 $41.45   12.313%   $46.5537   $46.55   $46.55   $46.60  
  Purchase #6 $126.91   6.820%   $135.5653   $135.57   $135.55   $135.60  
  Purchase #7 $201.94   5.389%   $212.8225   $212.82   $212.80   $212.80  
  7 purchase totals = $871.36       $949.7990   $949.80   $949.75   $949.80