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 $206.56   7.807%   $222.6861   $222.69   $222.70   $222.70  
  Purchase #2 $13.95   5.197%   $14.675   $14.68   $14.70   $14.70  
  Purchase #3 $181.59   6.562%   $193.5059   $193.51   $193.50   $193.50  
  Purchase #4 $67.89   11.238%   $75.5195   $75.52   $75.50   $75.50  
  Purchase #5 $224.65   12.476%   $252.6773   $252.68   $252.70   $252.70  
  Purchase #6 $181.80   12.302%   $204.165   $204.17   $204.15   $204.20  
  Purchase #7 $111.68   13.829%   $127.1242   $127.12   $127.10   $127.10  
  7 purchase totals = $988.12       $1,090.3530   $1,090.37   $1,090.35   $1,090.40