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 $202.76   12.764%   $228.6403   $228.64   $228.65   $228.60  
  Purchase #2 $10.88   5.433%   $11.4711   $11.47   $11.45   $11.50  
  Purchase #3 $152.72   12.145%   $171.2678   $171.27   $171.25   $171.30  
  Purchase #4 $47.91   6.273%   $50.9154   $50.92   $50.90   $50.90  
  Purchase #5 $74.32   10.353%   $82.0143   $82.01   $82.00   $82.00  
  Purchase #6 $89.83   4.864%   $94.1993   $94.20   $94.20   $94.20  
  Purchase #7 $118.84   8.811%   $129.311   $129.31   $129.30   $129.30  
  7 purchase totals = $697.26       $767.8192   $767.82   $767.75   $767.80