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 $70.68   6.862%   $75.5301   $75.53   $75.55   $75.50  
  Purchase #2 $33.40   13.308%   $37.8449   $37.84   $37.85   $37.80  
  Purchase #3 $41.53   3.571%   $43.013   $43.01   $43.00   $43.00  
  Purchase #4 $156.49   12.291%   $175.7242   $175.72   $175.70   $175.70  
  Purchase #5 $236.35   10.754%   $261.7671   $261.77   $261.75   $261.80  
  Purchase #6 $207.97   13.372%   $235.7797   $235.78   $235.80   $235.80  
  Purchase #7 $89.50   7.350%   $96.0783   $96.08   $96.10   $96.10  
  7 purchase totals = $835.92       $925.7373   $925.73   $925.75   $925.70