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 $34.45   3.213%   $35.5569   $35.56   $35.55   $35.60  
  Purchase #2 $199.52   6.266%   $212.0219   $212.02   $212.00   $212.00  
  Purchase #3 $77.64   11.772%   $86.7798   $86.78   $86.80   $86.80  
  Purchase #4 $204.91   10.736%   $226.9091   $226.91   $226.90   $226.90  
  Purchase #5 $204.56   6.804%   $218.4783   $218.48   $218.50   $218.50  
  Purchase #6 $142.84   12.140%   $160.1808   $160.18   $160.20   $160.20  
  Purchase #7 $209.50   12.347%   $235.367   $235.37   $235.35   $235.40  
  7 purchase totals = $1,073.42       $1,175.2938   $1,175.30   $1,175.30   $1,175.40