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 $190.91   10.310%   $210.5928   $210.59   $210.60   $210.60  
  Purchase #2 $164.77   6.596%   $175.6382   $175.64   $175.65   $175.60  
  Purchase #3 $153.64   9.268%   $167.8794   $167.88   $167.90   $167.90  
  Purchase #4 $64.94   3.298%   $67.0817   $67.08   $67.10   $67.10  
  Purchase #5 $168.92   5.467%   $178.1549   $178.15   $178.15   $178.20  
  Purchase #6 $95.59   11.603%   $106.6813   $106.68   $106.70   $106.70  
  Purchase #7 $122.67   12.700%   $138.2491   $138.25   $138.25   $138.20  
  7 purchase totals = $961.44       $1,044.2774   $1,044.27   $1,044.35   $1,044.30