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 $106.35   11.769%   $118.8663   $118.87   $118.85   $118.90  
  Purchase #2 $178.71   12.648%   $201.3132   $201.31   $201.30   $201.30  
  Purchase #3 $187.44   5.645%   $198.021   $198.02   $198.00   $198.00  
  Purchase #4 $157.96   3.745%   $163.8756   $163.88   $163.90   $163.90  
  Purchase #5 $127.92   5.342%   $134.7535   $134.75   $134.75   $134.80  
  Purchase #6 $223.42   10.253%   $246.3273   $246.33   $246.35   $246.30  
  Purchase #7 $199.52   5.366%   $210.2262   $210.23   $210.25   $210.20  
  7 purchase totals = $1,181.32       $1,273.3831   $1,273.39   $1,273.40   $1,273.40