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 $65.76   6.374%   $69.9515   $69.95   $69.95   $70.00  
  Purchase #2 $121.31   7.401%   $130.2882   $130.29   $130.30   $130.30  
  Purchase #3 $40.37   7.839%   $43.5346   $43.53   $43.55   $43.50  
  Purchase #4 $220.45   9.449%   $241.2803   $241.28   $241.30   $241.30  
  Purchase #5 $33.52   7.387%   $35.9961   $36.00   $36.00   $36.00  
  Purchase #6 $76.93   10.787%   $85.2284   $85.23   $85.25   $85.20  
  Purchase #7 $184.62   12.317%   $207.3596   $207.36   $207.35   $207.40  
  7 purchase totals = $742.96       $813.6387   $813.64   $813.70   $813.70