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 $60.28   11.694%   $67.3291   $67.33   $67.35   $67.30  
  Purchase #2 $24.83   12.133%   $27.8426   $27.84   $27.85   $27.80  
  Purchase #3 $97.98   11.210%   $108.9636   $108.96   $108.95   $109.00  
  Purchase #4 $187.97   6.582%   $200.3422   $200.34   $200.35   $200.30  
  Purchase #5 $63.53   3.440%   $65.7154   $65.72   $65.70   $65.70  
  Purchase #6 $72.80   11.434%   $81.124   $81.12   $81.10   $81.10  
  Purchase #7 $56.45   9.213%   $61.6507   $61.65   $61.65   $61.70  
  7 purchase totals = $563.84       $612.9676   $612.96   $612.95   $612.90