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 $91.96   10.640%   $101.7445   $101.74   $101.75   $101.70  
  Purchase #2 $80.59   6.628%   $85.9315   $85.93   $85.95   $85.90  
  Purchase #3 $76.34   6.377%   $81.2082   $81.21   $81.20   $81.20  
  Purchase #4 $96.47   12.689%   $108.7111   $108.71   $108.70   $108.70  
  Purchase #5 $199.57   4.211%   $207.9739   $207.97   $207.95   $208.00  
  Purchase #6 $172.76   11.681%   $192.9401   $192.94   $192.95   $192.90  
  Purchase #7 $243.50   11.873%   $272.4108   $272.41   $272.40   $272.40  
  7 purchase totals = $961.19       $1,050.9201   $1,050.91   $1,050.90   $1,050.80