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 $74.94   8.372%   $81.214   $81.21   $81.20   $81.20  
  Purchase #2 $132.87   11.352%   $147.9534   $147.95   $147.95   $148.00  
  Purchase #3 $241.84   11.399%   $269.4073   $269.41   $269.40   $269.40  
  Purchase #4 $234.52   10.445%   $259.0156   $259.02   $259.00   $259.00  
  Purchase #5 $45.29   6.816%   $48.377   $48.38   $48.40   $48.40  
  Purchase #6 $122.59   11.746%   $136.9894   $136.99   $137.00   $137.00  
  Purchase #7 $205.44   6.612%   $219.0237   $219.02   $219.00   $219.00  
  7 purchase totals = $1,057.49       $1,161.9804   $1,161.98   $1,161.95   $1,162.00