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 $96.60   11.469%   $107.6791   $107.68   $107.70   $107.70  
  Purchase #2 $126.96   8.358%   $137.5713   $137.57   $137.55   $137.60  
  Purchase #3 $43.70   13.674%   $49.6755   $49.68   $49.70   $49.70  
  Purchase #4 $99.25   8.752%   $107.9364   $107.94   $107.95   $107.90  
  Purchase #5 $189.98   6.727%   $202.76   $202.76   $202.75   $202.80  
  Purchase #6 $219.71   9.280%   $240.0991   $240.10   $240.10   $240.10  
  Purchase #7 $119.76   12.755%   $135.0354   $135.04   $135.05   $135.00  
  7 purchase totals = $895.96       $980.7568   $980.77   $980.80   $980.80