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 $59.75   9.764%   $65.584   $65.58   $65.60   $65.60  
  Purchase #2 $76.59   13.417%   $86.8661   $86.87   $86.85   $86.90  
  Purchase #3 $211.44   8.298%   $228.9853   $228.99   $229.00   $229.00  
  Purchase #4 $211.98   9.825%   $232.807   $232.81   $232.80   $232.80  
  Purchase #5 $187.31   10.190%   $206.3969   $206.40   $206.40   $206.40  
  Purchase #6 $147.43   13.658%   $167.566   $167.57   $167.55   $167.60  
  Purchase #7 $36.79   11.393%   $40.9815   $40.98   $41.00   $41.00  
  7 purchase totals = $931.29       $1,029.1868   $1,029.20   $1,029.20   $1,029.30