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 $206.53   6.353%   $219.6509   $219.65   $219.65   $219.70  
  Purchase #2 $69.88   8.156%   $75.5794   $75.58   $75.60   $75.60  
  Purchase #3 $63.48   7.661%   $68.3432   $68.34   $68.35   $68.30  
  Purchase #4 $135.45   7.347%   $145.4015   $145.40   $145.40   $145.40  
  Purchase #5 $246.46   12.583%   $277.4721   $277.47   $277.45   $277.50  
  Purchase #6 $184.60   10.790%   $204.5183   $204.52   $204.50   $204.50  
  Purchase #7 $68.33   7.325%   $73.3352   $73.34   $73.35   $73.30  
  7 purchase totals = $974.73       $1,064.3006   $1,064.30   $1,064.30   $1,064.30