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 $243.35   13.156%   $275.3651   $275.37   $275.35   $275.40  
  Purchase #2 $101.32   13.310%   $114.8057   $114.81   $114.80   $114.80  
  Purchase #3 $174.99   6.813%   $186.9121   $186.91   $186.90   $186.90  
  Purchase #4 $74.85   4.820%   $78.4578   $78.46   $78.45   $78.50  
  Purchase #5 $64.79   6.356%   $68.9081   $68.91   $68.90   $68.90  
  Purchase #6 $230.61   11.416%   $256.9364   $256.94   $256.95   $256.90  
  Purchase #7 $203.74   8.303%   $220.6565   $220.66   $220.65   $220.70  
  7 purchase totals = $1,093.65       $1,202.0417   $1,202.06   $1,202.00   $1,202.10