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 $92.95   6.459%   $98.9536   $98.95   $98.95   $99.00  
  Purchase #2 $22.33   11.279%   $24.8486   $24.85   $24.85   $24.80  
  Purchase #3 $179.56   4.334%   $187.3421   $187.34   $187.35   $187.30  
  Purchase #4 $245.29   9.331%   $268.178   $268.18   $268.20   $268.20  
  Purchase #5 $115.92   11.440%   $129.1812   $129.18   $129.20   $129.20  
  Purchase #6 $189.48   12.196%   $212.589   $212.59   $212.60   $212.60  
  Purchase #7 $199.74   9.784%   $219.2826   $219.28   $219.30   $219.30  
  7 purchase totals = $1,045.27       $1,140.3751   $1,140.37   $1,140.45   $1,140.40