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 $82.65   3.778%   $85.7725   $85.77   $85.75   $85.80  
  Purchase #2 $137.31   11.409%   $152.9757   $152.98   $153.00   $153.00  
  Purchase #3 $204.31   4.513%   $213.5305   $213.53   $213.55   $213.50  
  Purchase #4 $37.96   3.724%   $39.3736   $39.37   $39.35   $39.40  
  Purchase #5 $22.32   11.183%   $24.816   $24.82   $24.80   $24.80  
  Purchase #6 $204.73   9.743%   $224.6768   $224.68   $224.70   $224.70  
  Purchase #7 $135.25   7.576%   $145.4965   $145.50   $145.50   $145.50  
  7 purchase totals = $824.53       $886.6416   $886.65   $886.65   $886.70