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 $39.31   9.428%   $43.0161   $43.02   $43.00   $43.00  
  Purchase #2 $241.85   11.789%   $270.3617   $270.36   $270.35   $270.40  
  Purchase #3 $126.73   12.800%   $142.9514   $142.95   $142.95   $143.00  
  Purchase #4 $181.89   9.849%   $199.8043   $199.80   $199.80   $199.80  
  Purchase #5 $194.53   8.833%   $211.7128   $211.71   $211.70   $211.70  
  Purchase #6 $32.94   5.557%   $34.7705   $34.77   $34.75   $34.80  
  Purchase #7 $140.29   8.476%   $152.181   $152.18   $152.20   $152.20  
  7 purchase totals = $957.54       $1,054.7978   $1,054.79   $1,054.75   $1,054.90