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 $184.68   4.793%   $193.5317   $193.53   $193.55   $193.50  
  Purchase #2 $86.90   11.213%   $96.6441   $96.64   $96.65   $96.60  
  Purchase #3 $243.63   6.755%   $260.0872   $260.09   $260.10   $260.10  
  Purchase #4 $59.39   5.126%   $62.4343   $62.43   $62.45   $62.40  
  Purchase #5 $169.68   8.702%   $184.4456   $184.45   $184.45   $184.40  
  Purchase #6 $181.65   13.391%   $205.9748   $205.97   $205.95   $206.00  
  Purchase #7 $68.95   8.256%   $74.6425   $74.64   $74.65   $74.60  
  7 purchase totals = $994.88       $1,077.7602   $1,077.75   $1,077.80   $1,077.60