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 $69.46   5.410%   $73.2178   $73.22   $73.20   $73.20  
  Purchase #2 $234.63   4.642%   $245.5215   $245.52   $245.50   $245.50  
  Purchase #3 $46.40   11.869%   $51.9072   $51.91   $51.90   $51.90  
  Purchase #4 $240.59   11.852%   $269.1047   $269.10   $269.10   $269.10  
  Purchase #5 $89.40   7.711%   $96.2936   $96.29   $96.30   $96.30  
  Purchase #6 $75.59   12.461%   $85.0093   $85.01   $85.00   $85.00  
  Purchase #7 $204.90   6.604%   $218.4316   $218.43   $218.45   $218.40  
  7 purchase totals = $960.97       $1,039.4857   $1,039.48   $1,039.45   $1,039.40