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 $31.96   7.412%   $34.3289   $34.33   $34.35   $34.30  
  Purchase #2 $95.52   11.419%   $106.4274   $106.43   $106.45   $106.40  
  Purchase #3 $34.65   12.446%   $38.9625   $38.96   $38.95   $39.00  
  Purchase #4 $250.92   6.269%   $266.6502   $266.65   $266.65   $266.70  
  Purchase #5 $221.46   13.593%   $251.5631   $251.56   $251.55   $251.60  
  Purchase #6 $93.74   13.589%   $106.4783   $106.48   $106.50   $106.50  
  Purchase #7 $171.30   4.262%   $178.6008   $178.60   $178.60   $178.60  
  7 purchase totals = $899.55       $983.0112   $983.01   $983.05   $983.10