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 $60.38   8.602%   $65.5739   $65.57   $65.55   $65.60  
  Purchase #2 $186.54   8.315%   $202.0508   $202.05   $202.05   $202.10  
  Purchase #3 $212.97   7.352%   $228.6276   $228.63   $228.65   $228.60  
  Purchase #4 $56.65   12.679%   $63.8327   $63.83   $63.85   $63.80  
  Purchase #5 $91.78   12.270%   $103.0414   $103.04   $103.05   $103.00  
  Purchase #6 $18.49   11.406%   $20.599   $20.60   $20.60   $20.60  
  Purchase #7 $153.82   12.217%   $172.6122   $172.61   $172.60   $172.60  
  7 purchase totals = $780.63       $856.3376   $856.33   $856.35   $856.30