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 $216.77   4.364%   $226.2298   $226.23   $226.25   $226.20  
  Purchase #2 $67.93   8.419%   $73.649   $73.65   $73.65   $73.60  
  Purchase #3 $26.59   5.106%   $27.9477   $27.95   $27.95   $27.90  
  Purchase #4 $85.90   6.492%   $91.4766   $91.48   $91.50   $91.50  
  Purchase #5 $164.98   9.732%   $181.0359   $181.04   $181.05   $181.00  
  Purchase #6 $147.74   8.470%   $160.2536   $160.25   $160.25   $160.30  
  Purchase #7 $232.79   11.846%   $260.3663   $260.37   $260.35   $260.40  
  7 purchase totals = $942.70       $1,020.9589   $1,020.97   $1,021.00   $1,020.90