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 $178.95   12.702%   $201.6802   $201.68   $201.70   $201.70  
  Purchase #2 $69.37   12.178%   $77.8179   $77.82   $77.80   $77.80  
  Purchase #3 $169.68   6.809%   $181.2335   $181.23   $181.25   $181.20  
  Purchase #4 $23.47   13.412%   $26.6178   $26.62   $26.60   $26.60  
  Purchase #5 $238.76   5.458%   $251.7915   $251.79   $251.80   $251.80  
  Purchase #6 $201.61   8.374%   $218.4928   $218.49   $218.50   $218.50  
  Purchase #7 $27.68   4.717%   $28.9857   $28.99   $29.00   $29.00  
  7 purchase totals = $909.52       $986.6194   $986.62   $986.65   $986.60