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 $58.95   12.820%   $66.5074   $66.51   $66.50   $66.50  
  Purchase #2 $192.53   5.209%   $202.5589   $202.56   $202.55   $202.60  
  Purchase #3 $139.87   7.348%   $150.1476   $150.15   $150.15   $150.10  
  Purchase #4 $176.65   8.236%   $191.1989   $191.20   $191.20   $191.20  
  Purchase #5 $199.98   9.552%   $219.0821   $219.08   $219.10   $219.10  
  Purchase #6 $147.99   3.818%   $153.6403   $153.64   $153.65   $153.60  
  Purchase #7 $180.29   4.708%   $188.7781   $188.78   $188.80   $188.80  
  7 purchase totals = $1,096.26       $1,171.9133   $1,171.92   $1,171.95   $1,171.90