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 $37.52   3.502%   $38.834   $38.83   $38.85   $38.80  
  Purchase #2 $67.36   12.528%   $75.7989   $75.80   $75.80   $75.80  
  Purchase #3 $248.74   11.345%   $276.9596   $276.96   $276.95   $277.00  
  Purchase #4 $51.80   7.168%   $55.513   $55.51   $55.50   $55.50  
  Purchase #5 $45.72   12.567%   $51.4656   $51.47   $51.45   $51.50  
  Purchase #6 $113.53   12.731%   $127.9835   $127.98   $128.00   $128.00  
  Purchase #7 $241.88   11.451%   $269.5777   $269.58   $269.60   $269.60  
  7 purchase totals = $806.55       $896.1323   $896.13   $896.15   $896.20