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 $122.45   7.619%   $131.7795   $131.78   $131.80   $131.80  
  Purchase #2 $181.62   12.298%   $203.9556   $203.96   $203.95   $204.00  
  Purchase #3 $75.57   4.425%   $78.914   $78.91   $78.90   $78.90  
  Purchase #4 $247.62   6.193%   $262.9551   $262.96   $262.95   $263.00  
  Purchase #5 $60.48   6.682%   $64.5213   $64.52   $64.50   $64.50  
  Purchase #6 $177.85   13.735%   $202.2777   $202.28   $202.30   $202.30  
  Purchase #7 $198.85   6.687%   $212.1471   $212.15   $212.15   $212.10  
  7 purchase totals = $1,064.44       $1,156.5503   $1,156.56   $1,156.55   $1,156.60