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 $83.54   13.485%   $94.8054   $94.81   $94.80   $94.80  
  Purchase #2 $36.39   4.589%   $38.0599   $38.06   $38.05   $38.10  
  Purchase #3 $78.52   10.874%   $87.0583   $87.06   $87.05   $87.10  
  Purchase #4 $98.56   5.217%   $103.7019   $103.70   $103.70   $103.70  
  Purchase #5 $211.40   11.201%   $235.0789   $235.08   $235.10   $235.10  
  Purchase #6 $183.50   3.523%   $189.9647   $189.96   $189.95   $190.00  
  Purchase #7 $165.90   8.701%   $180.335   $180.34   $180.35   $180.30  
  7 purchase totals = $857.81       $929.0041   $929.01   $929.00   $929.10