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 $129.82   6.155%   $137.8104   $137.81   $137.80   $137.80  
  Purchase #2 $204.88   7.592%   $220.4345   $220.43   $220.45   $220.40  
  Purchase #3 $42.98   4.490%   $44.9098   $44.91   $44.90   $44.90  
  Purchase #4 $46.84   6.854%   $50.0504   $50.05   $50.05   $50.10  
  Purchase #5 $227.43   6.586%   $242.4085   $242.41   $242.40   $242.40  
  Purchase #6 $212.35   5.779%   $224.6217   $224.62   $224.60   $224.60  
  Purchase #7 $97.36   9.557%   $106.6647   $106.66   $106.65   $106.70  
  7 purchase totals = $961.66       $1,026.9000   $1,026.89   $1,026.85   $1,026.90