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 $64.97   9.844%   $71.3656   $71.37   $71.35   $71.40  
  Purchase #2 $189.96   13.478%   $215.5628   $215.56   $215.55   $215.60  
  Purchase #3 $231.30   3.573%   $239.5643   $239.56   $239.55   $239.60  
  Purchase #4 $14.37   9.502%   $15.7354   $15.74   $15.75   $15.70  
  Purchase #5 $187.91   11.508%   $209.5347   $209.53   $209.55   $209.50  
  Purchase #6 $172.60   4.841%   $180.9556   $180.96   $180.95   $181.00  
  Purchase #7 $244.33   10.227%   $269.3176   $269.32   $269.30   $269.30  
  7 purchase totals = $1,105.44       $1,202.0360   $1,202.04   $1,202.00   $1,202.10