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 $69.68   8.301%   $75.4641   $75.46   $75.45   $75.50  
  Purchase #2 $193.78   6.478%   $206.3331   $206.33   $206.35   $206.30  
  Purchase #3 $235.25   5.308%   $247.7371   $247.74   $247.75   $247.70  
  Purchase #4 $91.49   3.597%   $94.7809   $94.78   $94.80   $94.80  
  Purchase #5 $134.43   8.115%   $145.339   $145.34   $145.35   $145.30  
  Purchase #6 $235.72   12.849%   $266.0077   $266.01   $266.00   $266.00  
  Purchase #7 $24.27   7.638%   $26.1237   $26.12   $26.10   $26.10  
  7 purchase totals = $984.62       $1,061.7856   $1,061.78   $1,061.80   $1,061.70