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 $146.48   10.374%   $161.6758   $161.68   $161.70   $161.70  
  Purchase #2 $164.51   10.598%   $181.9448   $181.94   $181.95   $181.90  
  Purchase #3 $204.41   7.764%   $220.2804   $220.28   $220.30   $220.30  
  Purchase #4 $60.76   12.672%   $68.4595   $68.46   $68.45   $68.50  
  Purchase #5 $198.77   9.525%   $217.7028   $217.70   $217.70   $217.70  
  Purchase #6 $173.82   3.349%   $179.6412   $179.64   $179.65   $179.60  
  Purchase #7 $239.59   10.440%   $264.6032   $264.60   $264.60   $264.60  
  7 purchase totals = $1,188.34       $1,294.3077   $1,294.30   $1,294.35   $1,294.30