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 $85.52   12.465%   $96.1801   $96.18   $96.20   $96.20  
  Purchase #2 $80.98   11.403%   $90.2141   $90.21   $90.20   $90.20  
  Purchase #3 $136.72   9.270%   $149.3939   $149.39   $149.40   $149.40  
  Purchase #4 $166.56   5.555%   $175.8124   $175.81   $175.80   $175.80  
  Purchase #5 $181.40   11.701%   $202.6256   $202.63   $202.65   $202.60  
  Purchase #6 $174.72   12.711%   $196.9287   $196.93   $196.95   $196.90  
  Purchase #7 $173.37   11.695%   $193.6456   $193.65   $193.65   $193.60  
  7 purchase totals = $999.27       $1,104.8004   $1,104.80   $1,104.85   $1,104.70