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 $93.58   9.191%   $102.1809   $102.18   $102.20   $102.20  
  Purchase #2 $154.58   11.687%   $172.6458   $172.65   $172.65   $172.60  
  Purchase #3 $165.98   9.263%   $181.3547   $181.35   $181.35   $181.40  
  Purchase #4 $127.48   4.703%   $133.4754   $133.48   $133.50   $133.50  
  Purchase #5 $87.27   6.488%   $92.9321   $92.93   $92.95   $92.90  
  Purchase #6 $237.72   9.632%   $260.6172   $260.62   $260.60   $260.60  
  Purchase #7 $128.71   5.310%   $135.5445   $135.54   $135.55   $135.50  
  7 purchase totals = $995.32       $1,078.7506   $1,078.75   $1,078.80   $1,078.70