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 $245.56   8.789%   $267.1423   $267.14   $267.15   $267.10  
  Purchase #2 $201.75   13.156%   $228.2922   $228.29   $228.30   $228.30  
  Purchase #3 $60.98   7.771%   $65.7188   $65.72   $65.70   $65.70  
  Purchase #4 $203.27   7.720%   $218.9624   $218.96   $218.95   $219.00  
  Purchase #5 $187.84   8.245%   $203.3274   $203.33   $203.35   $203.30  
  Purchase #6 $250.84   9.636%   $275.0109   $275.01   $275.00   $275.00  
  Purchase #7 $194.75   5.193%   $204.8634   $204.86   $204.85   $204.90  
  7 purchase totals = $1,344.99       $1,463.3174   $1,463.31   $1,463.30   $1,463.30