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 $56.89   11.156%   $63.2366   $63.24   $63.25   $63.20  
  Purchase #2 $212.33   6.839%   $226.8512   $226.85   $226.85   $226.90  
  Purchase #3 $189.67   6.453%   $201.9094   $201.91   $201.90   $201.90  
  Purchase #4 $208.45   6.325%   $221.6345   $221.63   $221.65   $221.60  
  Purchase #5 $181.25   11.716%   $202.4853   $202.49   $202.50   $202.50  
  Purchase #6 $117.85   11.147%   $130.9867   $130.99   $131.00   $131.00  
  Purchase #7 $120.26   12.816%   $135.6725   $135.67   $135.65   $135.70  
  7 purchase totals = $1,086.70       $1,182.7762   $1,182.78   $1,182.80   $1,182.80