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 $113.90   4.797%   $119.3638   $119.36   $119.35   $119.40  
  Purchase #2 $50.80   4.255%   $52.9615   $52.96   $52.95   $53.00  
  Purchase #3 $154.98   9.404%   $169.5543   $169.55   $169.55   $169.60  
  Purchase #4 $127.42   8.673%   $138.4711   $138.47   $138.45   $138.50  
  Purchase #5 $173.52   5.713%   $183.4332   $183.43   $183.45   $183.40  
  Purchase #6 $238.32   11.868%   $266.6038   $266.60   $266.60   $266.60  
  Purchase #7 $175.84   7.769%   $189.501   $189.50   $189.50   $189.50  
  7 purchase totals = $1,034.78       $1,119.8887   $1,119.87   $1,119.85   $1,120.00