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 $176.98   8.289%   $191.6499   $191.65   $191.65   $191.60  
  Purchase #2 $94.83   4.483%   $99.0812   $99.08   $99.10   $99.10  
  Purchase #3 $216.84   8.506%   $235.2844   $235.28   $235.30   $235.30  
  Purchase #4 $196.53   6.220%   $208.7542   $208.75   $208.75   $208.80  
  Purchase #5 $182.78   10.710%   $202.3557   $202.36   $202.35   $202.40  
  Purchase #6 $104.73   8.163%   $113.2791   $113.28   $113.30   $113.30  
  Purchase #7 $11.60   9.188%   $12.6658   $12.67   $12.65   $12.70  
  7 purchase totals = $984.29       $1,063.0703   $1,063.07   $1,063.10   $1,063.20