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 $68.53   12.381%   $77.0147   $77.01   $77.00   $77.00  
  Purchase #2 $122.49   12.135%   $137.3542   $137.35   $137.35   $137.40  
  Purchase #3 $46.85   12.474%   $52.6941   $52.69   $52.70   $52.70  
  Purchase #4 $187.91   9.826%   $206.374   $206.37   $206.35   $206.40  
  Purchase #5 $144.29   3.738%   $149.6836   $149.68   $149.70   $149.70  
  Purchase #6 $228.28   10.838%   $253.021   $253.02   $253.00   $253.00  
  Purchase #7 $148.77   4.543%   $155.5286   $155.53   $155.55   $155.50  
  7 purchase totals = $947.12       $1,031.6702   $1,031.65   $1,031.65   $1,031.70