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 $225.97   6.740%   $241.2004   $241.20   $241.20   $241.20  
  Purchase #2 $28.90   6.834%   $30.875   $30.88   $30.90   $30.90  
  Purchase #3 $120.31   9.287%   $131.4832   $131.48   $131.50   $131.50  
  Purchase #4 $102.50   3.434%   $106.0199   $106.02   $106.00   $106.00  
  Purchase #5 $211.79   10.334%   $233.6764   $233.68   $233.70   $233.70  
  Purchase #6 $239.31   12.813%   $269.9728   $269.97   $269.95   $270.00  
  Purchase #7 $139.52   11.538%   $155.6178   $155.62   $155.60   $155.60  
  7 purchase totals = $1,068.30       $1,168.8455   $1,168.85   $1,168.85   $1,168.90