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 $69.55   7.152%   $74.5242   $74.52   $74.50   $74.50  
  Purchase #2 $69.67   5.419%   $73.4454   $73.45   $73.45   $73.40  
  Purchase #3 $241.49   10.440%   $266.7016   $266.70   $266.70   $266.70  
  Purchase #4 $120.42   5.643%   $127.2153   $127.22   $127.20   $127.20  
  Purchase #5 $203.73   7.148%   $218.2926   $218.29   $218.30   $218.30  
  Purchase #6 $181.65   13.151%   $205.5388   $205.54   $205.55   $205.50  
  Purchase #7 $92.85   7.225%   $99.5584   $99.56   $99.55   $99.60  
  7 purchase totals = $979.36       $1,065.2763   $1,065.28   $1,065.25   $1,065.20