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 $153.43   10.572%   $169.6506   $169.65   $169.65   $169.70  
  Purchase #2 $67.52   9.163%   $73.7069   $73.71   $73.70   $73.70  
  Purchase #3 $50.41   3.805%   $52.3281   $52.33   $52.35   $52.30  
  Purchase #4 $243.51   9.771%   $267.3034   $267.30   $267.30   $267.30  
  Purchase #5 $191.96   10.378%   $211.8816   $211.88   $211.90   $211.90  
  Purchase #6 $179.67   13.227%   $203.435   $203.44   $203.45   $203.40  
  Purchase #7 $60.77   4.355%   $63.4165   $63.42   $63.40   $63.40  
  7 purchase totals = $947.27       $1,041.7221   $1,041.73   $1,041.75   $1,041.70