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 $57.41   6.432%   $61.1026   $61.10   $61.10   $61.10  
  Purchase #2 $236.91   6.314%   $251.8685   $251.87   $251.85   $251.90  
  Purchase #3 $22.94   13.236%   $25.9763   $25.98   $26.00   $26.00  
  Purchase #4 $114.87   6.279%   $122.0827   $122.08   $122.10   $122.10  
  Purchase #5 $107.82   8.153%   $116.6106   $116.61   $116.60   $116.60  
  Purchase #6 $204.69   12.570%   $230.4195   $230.42   $230.40   $230.40  
  Purchase #7 $244.39   9.789%   $268.3133   $268.31   $268.30   $268.30  
  7 purchase totals = $989.03       $1,076.3735   $1,076.37   $1,076.35   $1,076.40