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 $56.65   11.223%   $63.0078   $63.01   $63.00   $63.00  
  Purchase #2 $149.27   11.606%   $166.5943   $166.59   $166.60   $166.60  
  Purchase #3 $234.44   7.828%   $252.792   $252.79   $252.80   $252.80  
  Purchase #4 $41.35   13.206%   $46.8107   $46.81   $46.80   $46.80  
  Purchase #5 $149.32   10.397%   $164.8448   $164.84   $164.85   $164.80  
  Purchase #6 $54.98   7.400%   $59.0485   $59.05   $59.05   $59.00  
  Purchase #7 $188.48   9.823%   $206.9944   $206.99   $207.00   $207.00  
  7 purchase totals = $874.49       $960.0925   $960.08   $960.10   $960.00